I'm a network administrator at a small residential college. Right now our firewall is set to have all network ports open by default, with a few exceptions. Unfortunately, bittorrent traffic has grown to the point where it kills our gateway server and I have no choice but to block it (I really would prefer not to). The only way to block bittorrent is to have ports closed by default.
Before I do this, I want to make sure that I don't take down xbox live, steam, playstation network, and games like call of duty, etc as collateral damange. This will end up leaving enough ports open that some bittorrent traffic still works - if you're really determined to get that latest black eyed peas song you'll be fine, but if you want to download (and share) every hip hop album or major software release in the last six months you'll have trouble. But it should restrict it enough that it no longer causes stability problems for the gateway, and of course also allow games.
I can handle other network service ports well enough, but I don't want to spend the rest of my career maintaining a list of network ports used for gaming. So where I can find a good, maintained list of these ports, preferably with an rss feed for changes, additions, etc?