i'll be stag doo'ing it up there in august.
depends on what your groups tastes are. I did a stag do a few years ago there.
if you like indie music then there are lots of great indie clubs etc, Canal street is the gay hub of manchester, but its a really good night out there; straight or gay.
theres also a few strip joints there as well.
if you like mountain bikes you've got some great tracks on the door step. paintballing, go karting, loads of stuff round there.