In games, $100 headphones will "image" better than any set of speakers you can find anywhere at any price.
It is amazing how much more you hear. You start to realize how good players can know exactly where you are at all times.
You aren't going to get chest pounding bass, but who needs a distraction like that in thick competition.
I use sony mdr 7506's. I like them a whole lot. They've got good isolation which is verrry important at LANs. They also have a lot of bass for a pair of headphones, everything is clear, and they are extremely rugged. I would highly reccommend them for lans, or the sony mdr v700's.
I've heard various models from sennheiser also. The HD600's are extremely nice, but completely unsuitable for LANs. I wasn't impressed with the rest of the models I heard.
jt