Savagezion said:
I'll second these as well as mention Galactic Civilizations 2 which is like Sins of a Solar Empire in setting (space) but Turn Based.
As well, I would recommend getting Civ 4 Complete and trying the Fall from Heaven 2 Mod. That way you also can check out Colonization.
Certainly good suggestions. Civ 4 becomes much better with the "Beyond the Sword" expansion and this also opens up the possibility of a lot of interesting mods. Colonization is an interesting and very different 4x game, not without serious flaws, but good fun overall. The Civ4 complete edition has loads of good content.