RTSguru.com has published a list of the best space-based 4x strategy games, and has included Galactic Civilizations II and Sins of a Solar Empire in their list!
What do you think about the choices?
http://www.rtsguru.com/features/160/The-List-Best-Space-Based-4X-Strategy-Games.html
2) Sins of a Solar Empire – I’m including this one even if the developers didn’t/don’t really consider it strictly a 4X game, they prefer the tag of RT4X. Which, I guess I kinda get their point; it was a blend of RTS and 4X after all. Whatever you want to call it, Sins is a blast to play. While it didn’t have as many different races and other depth as most 4X games out there, that actually improved the multiplayer side of things. Most 4X games don’t really cater to multiplayer, since they make for some really long games. The fact that Sins was a RTS/4X hybrid, it was quite a bit faster to play and lead to some fun multiplayer games. Ironclad released 2 ‘micro-expansions’ and one full-fledged stand-alone expansion that greatly improved and expanded the game.