Most people end up doing one of a few things on Kayle in Dominion:

Stacking AP -- Absolutely Horrible because AP doesn't significantly benefit Divine Blessing, Righteous Fury, or Intervention. You get a strong nuke with Reckoning and it's 1.0 AP ratio, but that's about it -- you get the exact same effect with stacking AD (since it also has a 1.0 AD ratio). In fact, Righteous Fury only has a 0.2 AP ratio but has a 0.4 AD ratio.

Pure AS / On-Hit-- This is a little bit better, but many people make the mistake of doing item builds similar to SR. Malady is just a terrible item for the current metagame in Dominion (where most damage dealers are physical, and if someone is tanking, they'll stack Armor over MR). Your splash damage is really good early game, but starts faltering late game. Adding a bit of AD goes a really long way.


The most viable build for the current Dominion metagame is a hybrid AS + AD / On-Hit Build.

Enough AS will give you the ability to push minion waves incredibly fast, and the AD/On-Hit will give you the killing power against almost every enemy champion in a 1v1 fight.


Changelog:
10/26/11 - Updated item build slightly, taking comments into suggestion.
11/2/11 - Added a few comments on item build, fixed a few typos.
11/7/11 - Changed masteries and summoner spells slightly to favor exhaust over promote. Updated runes slightly.
11/15/11 - Changed masteries to reflect revamped masteries for S2.
11/21/11 - Added in a little bit more in the Farming/Laning section. Also added some comments on AD vs AS in the intro. Also added Surge to 2nd tier summoner spells.
12/25/11 - Added in a very minor comment on Kitae vs Cleaver. +1 on Ionic Spark due to buff, but obviously take the anti-champ items when needed. Updated runes slightly.
12/26/11 - Updated with new runes again -- recommend greater quints of destruction (Armor Pen / Magic Pen) + Move Speed
1/17/11 - Updated for new patch (and removal of anti-Jax items). Mobafire still hasn't added the new runes into their database.

Reds:

Attack Speed x9 or Armor Pen x9
Greater Mark of Attack Speed is what I typically go with

Attack Speed helps your early game in farming, while Armor Pen gives you the edge late game.

Yellows:

Armor per Level x9 or Armor (flat) x9
Greater Seal of Defense favors mid-late game
or
Greater Seal of Armor favors early game

Survivability is key against the current metagame of physical heavy characters. I've also tried mixing these and have gotten good results.

Blues:

Cooldown Reduction (Flat) x9
Greater Glyph of Cooldown Reduction

This cooldown reduction gets your Reckoning close to perma-cast.

Quints:

Armor Pen, Attack Speed, Armor Pen/Magic Pen, Move Speed, Revival
Greater Quintessence of Precision are absolutely built for Kayle -- her abilities (and splash damage on E) are magic damage, and you get a ton of physical damage with this build too.

I've been experimenting a bit more and one, maybe two move speed quints helps her mobility issues in Dominion combined with the combo armor pen/magic pen quints (or revival, your choice).

Also, revival quints are pretty OP in Dominion, it really lets you get back to your lane super fast after dying (which especially helps in early game).

21/6/3 (as depicted above)

This build does not emphasize crit, as Kayle can't afford to build crit items without sacrificing attack speed. You want to get your attack speed up to about 2.0 as soon as possible to be effective in farming/pushing bottom and to maximize damage output during your ult.

Top Tier:

Great for defending 1v2 or tower diving. Note the absurd range on this -- you can interrupt enemy captures by popping this from afar.
Best Defense against Physical Dam bruisers given the current metagame. This makes 1v2 a lot easier.
Your pushing power is absurd and this helps even more in flipping a point quicker (especially while team fighting at a tower).

Second Tier:

Cleanse works well when fighting a CC heavy team, it keeps your damage output nice and high and allows you to clutch ult.
You are a little bit slow with this build, but you probably won't need it (given that you end up pushing waves rather than trying to ninja-cap points)
This works well for 1v1 fights and gives you a little extra damage even while dead.
This works well for pushing your DPS even higher and can allow you to cut out an extra AS item, however the cooldown is a bit long for Dominion. I wish this spell had an AD component.
You'll spend a lot of time at bottom for this playstyle, this can be the difference in your lane. Long cooldown makes it hard to take though.

R > E > Q > W

R ( Intervention) is your "i-win" button

E ( Righteous Fury) is essential for your early game and farming. It tails off near mid game and end game, however you really need the boost at start.

Q ( Reckoning) is your nuke & increased damage buff, open with this and unleash damage.

W ( Divine Blessing) is not great by any means -- it might be enough to keep you alive in a fight. The move speed buff probably won't catch you up to anyone.

Items #1 & #2: Core Starting Items:

These two should be your first two items -- Stinger is a great starting item with CDR and AS. The CDR on Stinger will get your E close to being perma-up, and the attack speed greatly helps your pushing power. Nashor's Tooth is terrible for Kayle in dominion, but Stinger is nice, cheap and gets you off the ground quickly.

I've tried a number of different starting items and builds on Kayle -- Berserker's Greaves gets you off the ground as quickly as possible after building your Stinger.

Boots work well as a second item because you'll be taking the bottom lane rather than rushing to the top.

Stinger is even better now that they reduced the cost on it.

Item #3: Choice -- Build more Attack Speed:

These items are cheap and supply good early game power -- they go a long way towards getting fed early.

General Purpose item, gives decent survivability and greatly enhances pushing power. I like this even more since they buffed it.
or
Anti Stealth Item, also works really well for chasing into brush. This item will cause you to shred through Akali.
or
Good against AP heavy teams. Not as much killing power as the other items, but works well for survivability. I wish there was a good equivalent for stopping AD.

Item #4: On Hit / AD:

This is the best item for Kayle if she has sufficiently high enough attack speed -- this will shred through enemies left and right. This also acts as a partial counter to thornmail becuase the on-hit effect is magic dam. Highly recommended vs tanky DPS.
or
Great on-hit effects and a ton of damage. Also gets your attack speed to where it's supposed to be. This is all dependent on opponent team makeup. If their team is a bit squishy, I'd get this over Kitae.

At this point you should be close to 2.0 Attack Speed and should have pretty good sustained DPS -- this is usually the point where I go from being able to 1v1 most champs to being able to dominate.

Item #5: Slow / AD:

This item works better than Frozen Mallet because of the huge AD boost, and you can activate the slow as required (since you also have Q as a slow). This also helps with staying in fights as long as possible, as you are a bit slow with this build.

Item #6: Choice -- Final Damage Item:

This gives you a little bit of leech for survivability (since by this point, everyone is starting to get tons of damage), and gives you more AD. Keep in mind that when you're invulnerable, you can get a ton of life back from leech.
or
Great on-hit effects and a ton of damage.

Your choice -- more damage or leech.

Final Upgrade: If you have excess gold and the game hasn't ended yet (very unlikely)

This finishes up your stinger, gives you more attack speed, more CDR (allowing E to be constant), and some AP (more or less useless).

A Few Comments on Item Build:

If you go for the recommended items on my build, you'll actually become pretty tanky between Ionic Spark and Entropy.

I also have built Entropy before my choice AS item in some games, and it works for certain situations. Play and experiment with the item order and use what fits you well.

I've also had games where I've faced Akali AND Jax and in those situations I usually build in the following order:
Stinger - Berserker's Greaves - The Lightbringer - Sword of the Divine - Phage - Sanguine Blade - Entropy - Nashor's Tooth

Other Useful Items

This may negate some of the AS you need in this build due to the active ability and it can work in place of the Stinger/Nashor's Tooth, however its hard to build early in the game while keeping Kayle somewhat viable.

I still can't work this well into my builds without gimping myself pretty badly early game, but it really allows you to cut out an extra AS item and go for more damage earlier.

Terrible Items

The AS boost is nice, but AP is a waste.
There are so many better AS items, and the majority of your damage is AD and not AP.
Expensive, Spell Leech is negligible for Kayle's skills and tons of worthless AP
Expensive, the AP half of things is kind of worthless, but the AS and CDR are a saving grace. Singer gets you most of what you need early game.
Crit is not a focus in this build. You need to build a lot of AS/AD/On-Hit items for Kayle, and you'd be either sacrificing AS or AD for Crit.

Farming / Laning

You're well suited to take the bottom lane -- you have incredible pushing power and your fights are more 1v1 and 1v2 fights.

The extra farm from the creep kills will get you gold faster than team fights and capturing points.

The constant pushing pressure you put on bottom tower will force enemy champions to leave the top/sides and come to the bottom to defend their capture point, which opens up the rest of your team to take top. You can take 1v2 fights pretty well with exhaust and/or garrison (although facing a hard CC makes it a little bit more difficult).

You are slow with this build, however unless you really need to rush to a control point for defense, it doesn't impact you that much. I usually end up pushing minion waves to capture a control point, and it usually flips faster than actually rushing to the point and capturing ahead of minions. If you have major speed issues, you may want to take 3x Move Speed quints instead of Armor Penetration.

Use your invulnerability bubble wisely -- you'll get to use it once every two fights/deaths or so. When used right, it's typically an "i win" button for a 1v1 (and sometimes a 1v2 fight). I usually time this right as an opponent champ starts their killing combo.

Usually after 1v1 and 1v2 fights, you're going to end up very low on health -- (ab)use the health boxes scattered throughout the map to your advantage.

Fighting Combos:

This provides a nice nuke, a slow for you to catch up to hit them with your ranged auto attacks
This gives you range on your auto attacks -- time this so that you maximize the duration of it during a fight (usually while your Reckoning is flying towards the enemy
Use this either for chasing, or mid fight to give you a slight HP boost while autoattacking
Use this when you're at low HP -- most enemies will keep on trying to attack you while you DPS them dead.

The biggest thing is to stand your ground in a fight -- You can go toe to toe with Yi, Jax, and a number of the other hard physical carries.

The champs that you have the hardest time with are the champs that run massive life leech // or have long attack speed debuffs -- AS/AD Sion, Nasus, TankWick etc.

This is my first guide -- so please give me suggestions.