Oh snap, i'm so glad i got in here before somebody else mentioned Battleships Forever.
http://www.wyrdysm.com/games.php BSF is pretty much the same as starfarer (or vice versa) except without the depth, amazing sprite work, great modding community (though the ship builders are INSANE), wonderful AI, and a million other things that make me love Starfarer. Ever since i played BSF the first time i've been looking for something that could match it... and man was Starfarer a pleasant surprise. Another awesome space game is Transcendence, it's also a very deep game in a very different way, with an excellent modding community and a fun story.
http://neurohack.com/transcendence/ All these links in my post, i feel like a spambot!
But yeah, check out BSF and Transcendence, they are highly recommended.
Edit: I forgot to mention the best part about these games: they're absolutely free!