I cruise and post on several Boxing Forums and newsgroups, but gotta say RossBoxing is the leader of the pack for Boxing (and related fitness topics.) No hot heads talking smack about the sport, No name calling or personal challenges. Just good friendly and intelligent folks who care about training and talking about it. I've recently been reading This forum and it also looks to be the same way. (In fact all the forums on this board seem well kept.)
..and I might add that Ross's training materials are also first Rate and highly thought of within the boxing community.