Check out the links I have listed for way more complete information. 111 Minna st has some good parties. I think it was funner a couple of years ago, now its gotten kind of crowded. These are also at 550 Space. The Top has some nice parties if you like a smaller, more intimate vibe.
Liquid is also cool.
I like tuesday nights. My favorite times are thurday night and sunday during the day-early evening. I heard the DJ on KZSU and he played an interesting set, so you might want to check it out.