Elite, Wing Commander, Freespace, Privateer, I-War, I-War2, X-series
X-Wing, Tie-Fighter, Shuttle, Darkstar one.
And the real nerd stuff Orbiter, Xplane with Spaceship One.
X3 Terran Conflict with all the community mods is pretty bloody good, but I always come back to Elite, the Zaonce-Lave-Leesti run is seared into my brain will have to see what X-Rebirth is like.
I-War 2 EoC had space combat and piracy to a fine art, closest thing to playing B5. Was stunning if you managed to take out a weapons convoy.
FTL looks really cool, reminds me of Infinite Space on the DS.