I recommend "X2: The Threat" or if you have a top notch computer (I don't) "X3: Reunion". Neglected gems - they totally blow Freelancer out the airlock. Sorry for that one. *hangs head in shame*

X2 Has:
- A much better trading system
- Buy factories and build up an empire
- Fly fighters through to carriers
It can also be got for ~£7.00

I'm lead to believe X3 is the same but bigger. Definitely worth a try!