Hi! This is my first build, so there probably wont be much detail, though i am open for suggestions :)

Pros:

Great damage
Lots of CC
AoE heal with short cooldown
75% damage reduction
He's a ****ing bull!

Cons:

Kinda slow
Can have kinda mana problems.

For red runes i go , because of the fact that both his real damaging abilities are magic damage(And his passive).

For yellow runes i go . You dont need these runes, but it really helps when laning in my opinion.

For blue runes i go . I go with scaling ap glyphs because they pass the flat ap ones in AP by far.

For quintessences i go . For the early boost.

For masteries i go the standard 9/0/21 caster build, going in offense down to 15% spell pen.
Make sure to get good hands and and by all means NOT perseverence http://www.leagueoflegends.com/board/showthread.php?t=219077, simple math ;)

Core items:

Boots:

Is usally the way to go, the CDR is amazing for Alistar. You should always get these boots, unless the team has 3 or more really hard CC (EG , , etc etc.) then you should get

If the opposing team has really hard AD, and they seem to be killing you easly, you should get a , If they have hard AP, you should probably invest in a . If everything is going smoothly, just go with the items i've already listed.

Colossal Strength(Passive):(Innate): Each time Alistar casts a spell he will be able to move through units and will deal 9 + (1 x level) + (+0.1 per ability power) magic damage per second to nearby enemy units and structures for 3 seconds. It deals double damage to minions and monsters.

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(Q):(Active): Alistar smashes the ground where he is standing, dealing magic damage to all enemies in the area and knocking them up for 1 second and stunning them upon landing for 0.5 seconds.
* Radius of AoE: 365
Cost: 70 / 85 / 100 / 115 / 130 mana

Cooldown: 17 / 16 / 15 / 14 / 13 seconds

Magic Damage: 60 / 105 / 150 / 195 / 240 (+0.6 per ability power)

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[W]:(Active): Alistar charges at an enemy and rams them, dealing damage and knocking them back (does not stun).

* Range: 650
* Knockback Distance: 650
Cost: 80 / 90 / 100 / 110 / 120 mana

Cooldown: 14 / 13 / 12 / 11 / 10 seconds

Magic Damage: 85 / 130 / 175 / 220 / 265 (+0.8 per ability power)

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(E):(Active): Alistar lets out a commanding war cry, instantly restoring health to himself, and nearby friendly units for half of that amount. The cooldown is reduced by 2 seconds each time a nearby enemy unit dies.

* Cooldown: 12 seconds
* Radius of AoE: 200
Cost: 20 / 30 / 40 / 50 / 60 mana

Self Heal: 60 / 90 / 120 / 150 / 180 (+0.4 per ability power)

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(Ultimate/R):(Active): Alistar lets out a wild roar, removing all crowd control effects from himself. He also gains bonus physical damage and takes 75% reduced physical and magic damage for a few seconds.

* Cost: 150 mana
Cooldown: 120 / 100 / 80 seconds

Duration: 6 / 7 / 8 seconds

Bonus Damage: 60 / 75 / 90

I start out with a point in (E) and taking a point in it after taking a point in (Ultimate/R).
And taking (Q) to E [W] every second time.

Just keep on using into for the harass, and when you feel the enemy has low enough health either
A: Use flash to push him into your turret and pulverize him there, the turret will devastate him.
Or B: Use Headbutt followed by Pulverize(You will night to do this fast, so that Pulverize kicks in) And if you need to turret dive, use your ultimate, heal whenever you can and try to stay on the enemy for trample to do damage. And obviously use ignite.

For Summoner Spells i go with and .

Possible other Summoner Spells to choose: , , ,

This pretty sums up my first build! Leave any suggestions, and stuff like that in the comments, and please, do vote! :D