Of recent titles tho i found the oblivion mod Nehrim to be pretty impressive in that regard.
Only an hour in but the starting dungeon really does a great job of keeping you on your toes and seeming like it could collapse around you at any moment.
The realiance on a hand held torch does wonders for the atmosphere and while its in the back of my mind that im never in any real danger since its the starting area and all i still occationally jump at a snarling beast somewhere up ahead in the dark.
Yeah, Wing Commander was FANTASTIC in terms of immersion, and it was the first "space sim" that truly gave me that Star Wars sensation.
But, you know what was even better - and to me represents the best space game of my experience:
Privateer
Damn, I miss games like that. Why the hell did they stop making them? Because of the joystick thing? How can people NOT like space games?
A very good premise and a high immersion has this space combat game:
Independence War 2: Edge of Chaos