Hey Mobafire- This is Tserraknight.
I've been reading around this site for a while and after reading so many good guides for champs, I figured I would try to put one out for you guys. I know I'm probably going to catch alot of flak for this one, because it is a really unusual one for this champ. But trust me, it works.
I've been playing Volibear since Day one of his release and I have tried a number of different builds with him, with scores ranging from 19/1/7 to as abysmal as 1/13/2 (that build will NOT be in the guide.) Anywho-ONWARDS INTO THE STORM.

My rune choices are fairly standard for tanky dps'ers. There are quite a few reasons for each one. Part of the choices are Flexibility. With the Armor Yellow and MR Blue and %health quint, if you need to switch to tank you have a nice base for it, or if you need more laning beef its there as well.
For a Offensive, the Arm/MR runes allow you to trade better blows, While ramping his frenzy better(throughout the game with both) allowing you to use it faster and make it hit harder passively with out sacrificing the tanking base.

Masteries are fairly standard here, nothing truly exotic. I went for the extra health, armor, and MR, again if you needed to make the last second, game started, still need to tank change, but not as flexible as the runes.
I will be experimenting later and seeing if I can find a more 15/15 split or something similar.
No, I did NOT take havoc, its a piece of ****. If each hit its for 1000, then it adds 15. The life steal from Vampirism helps much more, especially with a Bloodthirster or two late, or a Doran's blade or two early.

Doran's blade or Shield to start. I find it easier to get First Blood with the blade, but if your in a lane against some bullies or are solo, go shield.
Boots of Speed, next buy. Three choices here, depending on how your feeling. Merc's is always available against heavy CC, but, as you are naturally tanky you can survive some hard cc with out too much fear(even though it sucks). Your next choice is Zerker's greaves. ATKSPD is nice for frenzy and his ultimate, and it has the perk of being cheap. Lastly, Tabi is a choice if your getting bullied too hard. Also with tabi, you can still choose to go tank with out much hassle.
Then Zeal. It makes Q,W, and R all better.
Then an Ionic Spark. This plus Ult = LIGHTNING EVERYWHERE. Massive AoE damage that dominates team fights and minion waves. Plus frenzy's passive giving you huge ATKSPD allowing for fast stacks of what ever it is that makes Ionic, well, spark.
You should be doing fairly well at this point.
Follow with a phage into a frozen Mallet. After this noone will EVER get away from you. This also boosts your frenzy, works from your Rolling Thunder, Stacks with majestic. I need to test and see if the arcing from ult and or ionic slow. Haven't been able to test that yet.
Upgrade Zeal into Phantom. just more candy for most of your skills.
at this point you've got most of what you need. You can go a few ways now.
Another Phantom + a Bloodthirster gives a attack speed and life steal component making you VERY hard to kill, if your trading blows with lots of Melee.
Warmog's and Atma's is another popular choice giving you a ton of health and Ad and Frenzy will go nuts.
Finally you could go with Banshee's and Guardian if those mages are bugging you and your enemies can actually hurt you.
I like Phantom because of the move speed + rolling+ghost = dead what ever was going to run away. Even slippery bastards like Kassadin and Nidalee.

Skill Sequence is pretty simple. Frenzy. Frenzy. Oh yeah. Frenzy. Rolling Thunder and Majestic roar are ok, but Frenzy is your bread and butter. It ramps your attack speed through the roof, and it is effectively Garen's Ult on about a 20 second cooldown. It scales better and better as your HP grows.
Rolling thunder is useful for fling(singed players know whats up) as well as It is a get away (+15%) or a Gap Closer(+45%). It also resets attack timers, and deals bonus damage, procs frenzy, and works on turrets. All in all it's really good with a lot of utility.
Majestic roar has two real uses. Its damage is damage, no complaining, but its best used to fear minions out of your way to chase or flee(unit collision is annoying) and to slow Champions enough to let you hit with rolling Thunder so that you can get to the nomz.
Ultimate-Thunder Claws. This has a few uses too, not the least of which is feeling like a badass. Clears minion waves really quickly. Also...Aimed right, (it does prioritize champs) it can kill really weak champs under a tower by arcing the lighting, with out having to tower dive. Also, it makes you hit harder, and since its time based, gets much more dps out of this Attack speed build. It also does alot of damage in team fights, and when trading blows with champs, turns minion waves into free gold while letting you focus on whats important. Its much better in its subtleties than its active uses. Also fairly short cooldown so dont worry about using it if you feel you need to.

Everyone on here knows what spells do what.
Get Ghost for sure, then choose Exhaust, Flash, Ignite, or Heal on preference.

This build requires a little bit of patience in the beginning, a heavy reliance on your passive right off, (watch out for ignite that thing SUCKS for you) and then feeding (literally) your way to amazing games. I'll be working more on this guild as I get free time. Sorry to all this guide isn't as Pretty as Others but I'll get it there.