Battlestar Galactica related
Battlestar Galactica - The official site of the show. If you haven't seen the new Galactica, man, how can you call yourself a scifi-fan?
Galactica.tv - Interviews, articles etc. Fun reading.
Battlestar Galactica Online - A 3D browser-based MMO by Bigpoint Games.
Hard-Light Productions - The biggest Freespace community still alive and kicking. Home of Diaspora, The Source Code Project and a whole bunch of other interesting projects.
Other FS2_Open Engine games
The Babylon Project - The granddaddy of all games based on FS2_Open. Hours worth of excellent gameplay, all free for taking.
Wing Commander Saga - Wing Commander brought to life with FS2_Open. The campaign is over 50 missions long.
Fate of the Galaxy - A very promising Star Wars total conversion for FS2_Open. Shares some staff with Diaspora.
Beyond the Red Line - Another BSG project no longer in development. Many of the members of Diaspora worked on the two mission demo available from this link before leaving to make Diaspora.
Scifi-Meshes.com - Big 3d/2d art community, dedicated to science fiction. Quite a few of Diaspora devs are (semi-)regulars there.