Hacker Dojo in Mountain View. Great community. Membership is $100 per month. Around the corner from YC.

Citizen Space: http://citizenspace.us/

Sandbox Suites: http://sandboxsuites.com/

I worked on Pier 38 this past Summer in the Dogpatch Labs building. Pretty cool space. http://dogpatchlabs.com/

Founders Den has gotten some press recently:

http://www.foundersden.com/