I keep coming for two reasons- to help other people as the good folks of SR helped me, and to remind myself just how bad it really was. Both are important.
A few things that help me:
1) Remind yourself how bad a hangover feels.
2) Think about the last time you got drunk and really humiliated yourself.
3) Remember what a cruel master alcohol can be.
4) Imagine the future you'll have once you're sober.
5) Think of all the people you hurt with your drinking, and how much more useful you are to them sober.
6) Project yourself into the future. Imagine a year. Five years. Ten years. Are you thriving or laying face down in a gutter? Which do you want?