Stack Exchange based site for Ubuntu questions and answers.

Site for providing new stack exchange based sites based on voting.

gallery of sites built using StackExchange - this is a good place to check for Q&A based community sites.

Services site for StackExchange website Q&A service

Community Knowledge Exchange behind Stack Overflow. It's the basis for sites like SuperUser, StackOverflow, and ServerFault. Not free but not unreasonable.

Stack Overflow is a programming Q & A site that's free

Server Fault is a Q&A site for system administrators and IT professionals that's free

Doctype is a free question and answer site for web designers

Wiki/User site for StackOverflow, ServerFault, and SuperUser sites for fixing/answering questions specifically about those sites.

Super User is a Q&A site for computer enthusiasts that's free. Excellent resource for anyone with computer questions about software or  hardware