The Midwest Clinic - International Band and Orchestra Conference. If you can't make it to Midwest, check out their list of Clinic Handouts - a vast collection of handouts (downloadable in pdf format) from clinicians from 2000-present.
BASBWE - British Association of Symphonic Bands and Wind Ensembles
United States Air Force Band
United States Air Force Band of Liberty
United States Army Band "Pershings own"
United States Army Bands
United States Army Field Band
United States Coast Guard Band
United States Marine Band "The President's Own"
United States Military Academy Band (West Point)
United States Naval Academy Band
United States Navy Band
United States Merchant Marine Academy Band
Washington D.C. Service Bands: Can You Afford Not to Audition? -An article by Brent Philips in the Online Trombone Journal
Military Music Web Site - CDs of US military bands, orchestras, choruses
The Great American Brass Band Festival - held annually in Danville, KY in June
IBEW - The Internet Bandsman's Everything Within - a phenomenal set of brass links on the web site of The Harrogate Band, a British brass band: books, journals, bibilographies, publishers (including sellers of sheet music), services & supplies, music software, sounds & sampling, recordings, recording companies, vintage and secondhand recordings, brass on radio & TV, videos & DVD, recording studios, musical reference, music technique, music education, theory, general music reference. An incredible collection of links, but there are a number of dead links, making you wonder if they collapsed from exhaustion after setting it all up and haven't been back...