Another vote for the Freespace 2 Open Source Project, which is essentially an open-source mod of the original Freespace 1&2 with a great deal of enhancements and an active community with additional mods and such (although I have to admit, I have only dipped into that thus far, but what I saw was very promising
Also an additional vote for the X-Games, I personally like X3: Terran Conflict, the latest one, but they are all solid, if a bit complex and time-consuming (also has a vibrant community, they have some good tutorials and resources, use them because the game is kinda bare in that regard.) If you have not tried them yet, there is a collection of all of the games called X-Superbox (or something like that) which should give you the whole enchilada
Also, if you like a little retro, but do not want to go all the way back to Elite, I personally highly recommend my probably all-time favorite
"Wing Commander: Privateer". It uses the Wing Commander setting and universe, but puts you into the role of a freelancer pilot, where you take on missions, ferry trade goods around, deal with pirates, all the good stuff. It is from the early 1990s (so retro, but not totally retro
and there is a great open-source version which you can check out for free here:
Wing Commander: Privateer Gemini Gold [http://privateer.sourceforge.net/]