Bela Fleck and the Flecktones - My favorite musical group. Their music is practically unclassifiable, but they call it blu-bop (combination of bluegrass and bebop). They're a jazz group basically, thought they cover everything from reggae to latin, consisting of banjo, bass guitar, sax, and drumitar, and they're one of my biggest influences.
Robert Walter's 20th Congress - A fantastically good jazz/funk band consisting of keys, sax, bass, percussion, and drums. Gradually becoming another big influence for me, but besides that, it's just really fun music.
ITEA - The International Tuba/Euphonium Association, formerly T.U.B.A. (Tubists Universal Brotherhood Association). The Mecca of all things tuba and euphonium, with lots of tips from pros, among other things, and home of the official Tuba Press - the largest publisher of music for tubas and euphoniums.
TubeNet - One of the longest-running tuba related websites on the net, it is home of the world-famous TubeNet BBS. If anyone knows the answer to any of your tuba/euphonium questions, it's the people on this board.
University of Florida - 'Neath the orange and blue victorious, our love shall never fail. There's no other name so glorious, all hail, Florida hail!
UF Bands - Home to the Pride of the Sunshine as well as the Wind Symphony, Symphonic Band, and Concert Bands. It also contains information on the annual conductor's symposium. Also, find concert dates and high-quality recordings of high-quality music by the high-quality musicians of the University of Florida past and present.
The Internet Archive - This is the home of the Internet Library. It houses thousands of eBooks, films, and live music files, more than one person probably could go through. The live music archive even includes music from Bela Fleck and the Flecktones and Robert Walter's 20th Congress. I'd recommend the Flecktones' 2/11/03 show, and Robert Walter's 10/23/03 show. But you definitely should read the site's FAQs before exploring.
Should something else be listed here?