Alistar is not only a great tank but fantastic "support" as well. He doesn't kill too often but he does make people dead. He is an amazing lane partner because not only is he an amazing bodyguard but he doesn't need a lot of gold coming in early to be viable. Stay up front while your squishy lane partner farms last hits. If anyone comes close Headbutt them away. If they are being belligerent Pulverize and then smack them a few times before they get out of range to make them a little more wary of trying to harass your lane buddy. Spam your heal. By level three you should have Pulverize and Headbutt, flash in for your combo and (assuming your partner has exhaust) it should be a guaranteed kill.

Buy Boots of Mobility. If Flash and Ghost are on cooldown you can still come in from the side very quickly with BoM, plus you can get from lane to lane or cut off a runner (from a fight you were headed to) much easier and do what you do best, make people dead.

And don't forget, after a successful combo that results in an enemy being killed you must immediately "/all MOOOOOO"

Just know this when you jump into solo que ranked with Alistar, prepare to get all kinds of qq, rage, and "omg we failed because he picked Alistar" even though u played solid.

Stop kidding yourself. I used to main as alistar and he is nowhere near as good as he used to be. There are just too many champs that do his job and better. The only thing alistar has is his heal and that is in need of serious buffs. No heal, not viable.

I am learning to play him because I want to be able to play a "tank" for my team in case rammus, shen, malph have been banned or taken. That is the main adv of being a good alistar. nobody plays him. He's a better team disruptor than shen or rammus (though overall they are still probably better) and if you put teleport on him you can really take some cheap shots at towers cause you mow towers down fast!!!! Also he is not very item dependant so you can do lots of different things to adapt during a game. Shen and Rammus and Malph are much more item dependant. You just have to know your champ and what they are capable of. If you are expecting him to do certain things that he's not good at then your items will be all f'd up and your gameplay will suck. Think of Alistar as a Janna like Tank.

Get items that have movement speed.
Swiftness boots, force of nature, lichbane, SHURELIAS REVERIE (active) ! and you will have a shtload of regen and movement speed to land your stun.
Alistair is nice.

Alistar is also a nice counter to panth while laning, especially when the panth ranks up hss quickly. If he tries to combo you...pulv/head butt as soon as stun ends. If he goes for your lane partner, you can prevent the stun from landing if you pulv if his leap takes him in range of your pulv, or you can simply head butt him away as soon as he lands. Imo, he's one of the best (if not the best) babysitters in the game when leveling heal first.