Since there aren't many active topics on this board and I'm bored (ha-ha), I'll enquire as to why no-one mentioned Operation Flashpoint here - it's brilliant fun over a LAN as long as you can get a few players together.
Having said that, I've had perfectly enjoyable matches with just one other person, sneaking our way into towns and stuff.
I guess it only works if the friend is reasonably good at the game.
Although I'm entirely against skill discrimination in shooters, I'd imagine OPF just gets frustrating for those who die within 30 seconds of a fight breaking out
Freelancer is great for LAN gaming, because you can basically just join forces and go on epic missions.
At the moment, though, king of my LAN sessions is the marvellous DEFCON. It runs on basically any computer from the mid 90s onwards, and the games can last anywhere from 30 minutes to 6 hours(!). There's something to be said for the perverse tranquility of watching nukes fly over the atlantic ocean in realtime.