Apple Computer - OK, so I am somewhat religious about them...
International Trumpet Guild - everything you ever wanted to know about the trumpet

Yamaha Trumpets

Blackburn Trumpets - another fine custom trumpet craftsman
Lawler Trumpets - custom trumpet builder and maker of my B-flat

Schilke Trumpets

The Schilke Loyalist- great website all about Schilke trumpets

Jeff Purtle- great website with many articles about Claude Gordon (and lots of other stuff!)
Robert King Music - A great place to find your brass music

Hickeys Music - Another good place to buy music online

The Breathing Gym - great stuff!  Not only very informative, but also entertaining