JoshK:
I mostly use a peer to peer network called furthurnet (
www.furthurnet.org), which is reasonably efficient.
Recently I've been grabbing a lot of concerts using the bittorrents system, which is really fast, but the shows are only up for a few days so you have to grab them fast. Good starting points are:
http://digitalpanic.org/bt/index.phpand the forums at sharing the groove:
http://www.sharingthegroove.org/msgboard/Etree is a loose organization of private ftp boards, good if you can find an open slot.
www.etree.org. Their database is a great place to find out info about a show and maybe where to get it:
http://db.etree.orgFinally, and certainly not least is the internet archives. There are movies, music and a whole bunch more here. This may be the best place to start (click on the audio tab):
http://www.archive.org/There are also band specific ftp sites and mailing lists, from the big guys (The Dead, Phish, Bob Dylan, Neil Young) to more obscure (Gene Clark, Roy Buchanan).
If you get into it for a while, you will probably get into trading concerts by snail mail. There are tons and tons of places where people maintain their tradelists. Mine is at
www.tapercities.com and
www.phishhook.com is maybe the biggest such site.
All of the above deal only in taper friendly bands. Trading of official releases, charging cash or extra blanks, etc. are extremely frowned on.
Enjoy.