Alistar is really only vulnerable from lvls 1-5. Once you get ult just keep enough mana and your golden (no not the skin, but that 2).
My favorite rune set-up to run on him is:
armor pen red, clarity yellow, flat cooldown blue (with 1 cooldown per lvl blue), and 3 movement speed quints.
Then i go 9/0/21 to hit 9% cd on masteries, and get a nice movespeed bonus. There are many many other ways to play him, but that tends to work the best for me if I had to baseline my mixed play with him over the course of 400+ games.