Most of them are quiete nice and entertaiing, but I wouldn't dare to recommend you anyone without knwoing a Little more about what are you loking for (startegic/operational/tactic game, space combat/"ground" combat (undersatning ground as non-space, so tropos instead ofs starship), duration, etc...).
If you're looking for a ship-to-ship combat, quite close to CT:LBB2 taht can be played in an afternoon (even several games in a single afternoon) I'd recommend you
Mayday.
If you're looking for a man-to-man tactical combat game, you can choose among
Snapshoot or
AHL. Snapshoot is more RPG oriented, using practically the same rules as LBB1 on a small ship, while
AHL is more wargame oriented, using a different system and thought for more men in a larger ship. It requires more time and larger table to play. Personally, I like it more tan
Snapshoot, but that's purely a matter of taste (you'll also need to print quite more mapboards and counters than
Snapshoot).
If you like more strategical games, if ground based you have only
Invasion Earth. It's quite a good game, but you'll need some time to play it (don't expect to finish it in an afternoon).
For strategic fleet game, there are
FFW or
Imperium (I've never played
Dark Nebula, but for what I've read it's the same system than
Imperium with a different setting).
As for
FFW, I would not call it purely strategical, more as operational, as, while the troop scale may be so, the time scale (1 week) and the fact it portrays only the military part (no production, no control over reinforcements, etc.) precludes me to see it as fully strategical. Likewise, don't expect it to recreate the FFW too close (no long time consuming sieges or planetary invasions, that used to be resolved quite quickly when compared with OTU history). It is quite good a game, nonetheless, but, again, don't expect to finish it in an afternoon or two.
Imperium (and I guess
Dark Nebula, if it is so close to it as I've read here) are more fully strategic, as your focus there is the control of the territory to have better production and, not only wining the current war, but also to prepare for the next one. You can probably play a single war in an afternoon, while the full campaign can tak quite longer.
I have not played any other Traveller Wargame, but I hope that will help you.