9x Greater Mark of Insight

I take magic penetration runes because each of the proc-based items deal additions magic damage as well as your two damage-dealing abilities. 8.5 mpen coupled with the 20 Mpen from Sorcerer's Shoes will grant a flat magic penetration of just under 30, which will almost completely nullify the MR of squishies like Ashe who often fail to build magic resistance items.

9x Greater Seal of Resilience

Flat armour seals are always effective on junglers and even laning because it reduces the damage you take from neutral minions and early game harassment from auto-attacking champions. I take these seals on almost every champion I play for their early game value.
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9x Greater Glyph of Shielding

I take per level runes because for magic resistance because they offer the most benefit late game when most casters pick up large amounts of AP, and you will need all the help you can get surviving Nether Grasp, Summon: Tibbers, Transfusion, Dark Matter, and many more deadly spells that scale well with AP. The per level runes will grant almost double the magic resistance as flat ones, all you need to do is make it to level 10 and you've already reached the turnover point at which per level runes surpass flat ones.

For Warwick i recommend Smite and Flash. Smite cause for me, every jungler must take it and Flash because it is very usefull.

Smite

Every jungler must take smite. I don't care what anyone says about how well they can jungle without it, it is one summoner spell that is invaluable to the team from levels 1 to 18. It helps you take blue buff in a shorter time, blast the pesky blue wraith, and break down the difficult early red lizard. In late game it will secure dragon for your team, finish baron so no enemies can steal it, and even allow you to take the unaware enemies' buffs and gold.

Exhaust

I like to take Exhaust because it is the definitive anti-AD carry/DPS spell that will stop that fed Vayne from wrecking your team or that sly Corki from targeting your carry. It is also a useful escape in the event of a failed gank where suddenly the tables have turned. Pop exhaust on their damage dealer, take a quick Hungering Strike, and walk away like nothing ever happened. More importantly however, is the ganking power of exhaust. Before level 6, Warwick is an extremely weak ganker, and exhaust will help tremendously to secure a kill for your lane, don't hesitate to use it!

Flash

This spell is useful for a number of reasons and most people swear by it. On warwick, Flash -> Infinite Duress is an extremely lethal combination that allows little to no escape for an unsuspecting victim when paired with a teammate's CC, particularly useful when ganking lanes for that extra reach on your ultimate to keep them out of their tower range and closer to your teammates. Take this spell if you like it, I think it equally useful compared to exhaust, it just has a pretty long unmitigated cooldown, so use it wisely.


Ignite

I've seen Warwicks packing Ignite but I really don't think it's all that necessary on him. Here's why: you're already one of the best chasers in the game, if you need just a few more ticks of damage you can run up to them and hit them yourself. Sure it's useful for making that Tryndamere pay for his spin into your team, thinking he could just Undying Rage and get out of there alive, but the fact is it doesn't help your role as an anti-carry as much as summoner Exhaust and lacks the overall utility of Flash, and chances are at least two of your teammates already have it because it's a very popular summoner spell. Case in point: better leave it to a laner.

Ghost

I personally think it's a bit redundant with your passive Blood Scent but at early levels it would make ganking and positioning much easier. With only one available summoner spell however, I think you're better off taking exhaust or flash just because of sheer utility and usefulness in teamfights where Ghost trails off. That being said, it is very useful for escaping if you can successfully juke or dodge the enemy CC or targeting, and in my opinion is a summoner more suited for skilled players, although some may disagree.

Teleport

Great spell if you're a solo or middle lane champion but sadly you are neither, you are a jungler, and maybe if you're really crafty you can teleport to your wards in the top or bottom rivers for a gank to tell the world about, but the 300sec cooldown will make that quite infrequent. I simply like a little more utility in my summoner spells for late game teamfights, and this spell lacks that.

Cleanse

I like this spell, I think it's great for escaping the unavoidable focus of an entire team's CC when they realize you have significant damage output with this build. Take this if you like it, don't take it if you don't, exhaust or flash are both more usefull in my opinion.

Clairvoyance

Fantastic spell for at least one person on your team to have. Short cooldown and great utility, but better suited for your support. You should already be warding all over the central river and you have only got one optional summoner slot anyway, better not waste it on redundancies.

Clarity

I personally don't think this spell is all that viable at any point in the game, granting instant mana to yourself and allies is useful, but definitely not when you're in the jungle by yourself or when you have blue buff up for most of your mana-starved time.

Heal

This spell has been buffed tremendously to the point where I take it when in bot lane as an AD carry and even with some supports. It's just that good now with the improved scaling. However, you need a summoner that can assist your ganks, and this is more for the lane sustain than that, take exhaust or flash over this.

Revive
I think this spell is absolutely useless, end of story. It doesn't really help at all, and if you're dying enough to make this spell useful, then you're just not a good enough player in the first place.