The New dead.net
If you haven't checked it out yet, there have been some great additions with the recent revamping of the Grateful Dead's official site.
The beauty lies in the Taper's Section, which has a sort of "this week in concert history" section, which includes hours and hours of MP3's from shows throughout the band's decades of touring. There are a lot of 45 minute "Drums" versions, and some of it is pretty rough, but it's also a great resource and a blast to listen to some of the rarer songs.
And bless their little hearts for even including a feed. It really couldn't get any easier than that.