I'm a big fan of the C&C series, just love all those intricate battles. I tried to play over the net a few times but found I was being totally destroyed in a few minutes by 5 year olds from the other side of the world.
I have also been playing Neverwinter Nights (RPG) for a few years on and off and still haven't finished, a fascinating game to get you thinking and a couple of good punchups thrown in.
Cheers