Here are my recommendations of where to buy most of the products I review on this blog.
Instruments
http://www.wwbw.com - Most main brand instruments are sold here.
http://www.jimlaabsmusic.com - Schiller.
http://www.bigbottommusicnw.com - Sells the same euphonium as Jim Laabs Music but for $185 less. You can't beat Al's prices.
Mouthpieces
http://www.monette.net - Its best to get Monette mouthpieces straight from the source.
http://www.wwbw.com - Again, most main brand mouthpieces are sold here.
Instrument Stands
http://www.herculesstands.com - The best trombone stands you can get, in my opinion, come from HERCULES.
Music Stands
http://www.protecmusic.com - These guys really are the way to go as far as music stands go.