Schema

http://sqlserverpedia.com/wiki/Understanding_the_StackOverflow_Database_Schema Notes about schema used by StackOverflow.com and related websites. It is very simple, only several tables used. (most likely because there are performance problems with joins)

http://www.livejournal.com/doc/server/ljp.dbschema.ref.html basically raw schema in html with some comments

http://www.databaseanswers.org/data_models/index.htm useful data model samples