[joerich]

This was a really complete answer. Just to not repeat and complete it with a couple of new things:

-You might get some interesting and fun things in here: California Academy of Sciences and The Exploratorium. Every Thursdays they have special events.

-This is another website where you can find something: http://www.sfweekly.com/

If you want to socialize www.meetup.com (already told by Jemaclus) is great. You can also organize or find meetups to programme instead of programme alone for example. There are meetups for whatever think you want to think, so just try some of them until you find something and some people you like!

[Jemaclus]

I can't believe I forgot to mention Nightlife at the California Academy of Sciences on Thursday nights! GREAT program!