just fyi, the games you've mentioned are space strategies. Space sims are different, more akin to a tactical FPS in spaceships. You're going to get a lot of different suggestions in a different genre than you intend.
As far as 'space sims' go, Freespace 1 and 2 are glorious,glorious games. Freelancer is also a lot of fun, and X3 is good as a hypnotic sleep aid. OK that's cruel, I do enjoy X3, but it's very relaxed and sedate, but... does allow you to fly a capital ship, which most space sims won't let you near for fear that having a lot of firepower might be fun!