Search Vorpike for reference, the masteries changed a bit since I made this, I'll be editing in a bit.
EDIT: Kage's Pick is now called Spellthief's Edge
With the new 365 gold items, buildable into a better version for 850 (485 more), this leaves 150 gold if you have the mastery (+40 gold), enough for two wards.
Of course, you should keep in mind that they build into, Ancient Coin into Shurelia; Kage's Pick into Twin Shadows and Shard of True Ice; Relic Shield into Face of the Mountain...but you can always sell it at the end.
Kage's gives gp10, ap, mana regen and pick pocket, so get it for ranged supports that use mane (Soraka, Sona). Relic gives hp/hp regen and let's your autos insta-kill minions below 200 hp, giving the gold to a nearby ally as well, but it doesn't give gp10, Face of Mountain scales on hp, so get it on tanky supports (Leona, Taric), and keep using it on the siege minion. Ancient gives health and mana regen, and no gp10, you get gold everytime a minion you didn't kill dies near you. This is for if you play passively (or Thresh, who doesn't need ap or hp), also, this goes to waste if your adc keeps dying/also recalling, as you end up last hitting instead.
You can also get Kage's for other lanes, as it's free gold and the most gold efficient mana regen and ap item, but your pickpocket gets disabled if you last hit, so use right when you get to into lane, and last hit at the very last moment, this also pushes your lane less. Relic also works on the adc, as you get gold efficient hp/hp regen, and you give your support free gold. I suggest you build it into Targon's Brace until you're always away from your team.
Trinkets are free and you sell them for another one (goes on cd), they upgrade at level 9 and can be upgraded after that for 475.
Sweeping Lens: Basically a short oracle's elixer, good on jungle to clear wards when you gank
Scrying Orb: Short range clairvoyance that only lasts a second, good on supports, as you'll have ruby sightstone and get the ward limit anyways. You can start the game with Warding Totem, but sell it later. You can also get it on mid, because you either ward both bushes or neither, just don't push and watch for the obvious opponent charges. The purpose of this trinket is when you're chasing someone, you want to know which way they went...pretty op, and if you have a jump, you can use it on neutral monsters. If timed right, for monster steals.
EDIT: This trinket's actually pretty useless, it only gets decent range at level 9 and after 475 upgrade...just get the ward one.
Warding Totem: Just a ward, can get upgraded to vision ward (should get one or two of these on your team, and put them bushes in your jungle, destroying enemy wards, warding, and there's less chance of your enemies killing them, you can also use them as bait).
AD page is pretty obvious, get Double-Edge if you're melee and champion related ones if you're laning, like Executioner and Block, when in doubt with getting dps or cdr, get cdr it's .25% more.
The first AP page is for the heavy mana users (Ahri, Karthus) (and blue getters), the one point on movement is important as it puts you on par with the faster, non-ap-burst champions, also, getting hp regen equal to 10% of your mana regen saves you a lot of recalling (esp. Veigar).
Support page utilizes maximum income while having defence to meat shield with. You can take off one point on movement and get Scout.
ADC is like S3, with crit and ad speed mastery (as opposed to melee ad).
Tanks are even deadlier this season, with movement, more hp regen, armor and magic resist. Since there's no summoner spell masteries to mess up your tree, go 0/27/3, getting hp regen masteries if you have a hp regen spell (Shen, Zac), if not go with the second page
When jungling, don't get any enemy champion related spells, for obvious reason, not even Executioner, your is to not die...or let your allies die when you gank, so get defense masteries such as Oppression, taking less damage when you use red on your enemies.
Since AP masteries demand getting Executioner to move up the tree, just ignore and get defense, also AP junglers tend to be slower/no speed buffs/no initiates. Get either Oppression of Swiftness, depending on how much (soft) cc you and your team has, and how much slow the enemy has (most ap junglers don't have soft cc (meaning they can still attack you)).
Manaless AP just shifts the 9 utility points to defence.
AD Dominion does the opposite; shift defence to utility, because you need speed and summoner spell reduction, since you should have ghost and flash, combined with Distortion boots, your spells come back really fast, which, because they're movement spells, may save you the game.
The last page is for manaless supports (Shen) or supports that don't use that much mana/you have mana runes/items.