I know this is an old thread; but I hope folks are still paying attention. I was surprised no one posted one of the best space combat games EVER. It is Mac compatible (in fact, compatible with Mac, Windows, Linux, and now will play on an android phone). It even runs (beautifully) on my Kindle Fire:
Vendetta Online
http://www.vendetta-online.com/
Yes, it is subscription based. If you pay month to month, the cost is $9.99 per month. The cost decreases if you pay for bigger chunks. I am a big fan of Freelancer and, as such, truly enjoy Vendetta. An MMORPG, it employs a twitch based combat system. It is not a strategy game (YAY!!!!!!) - it does not require the micromanagement that such games require. In VO you can pursue mining, trade, you can be a BADA$$ combat pilot, or even a pirate. Some players are very into the RPG angle, some are more dedicated to combat. If you like this kind of game, there is something for everyone.
For big fans of space games, here are two additional resources to investigate:
http://spacesimcentral.com/
and:
http://spacegamejunkie.com/
Both are comprehensive, up to date, & well researched. Have fun. See you in space!