IMSLP/Petrucci Music Library - Free Public Domain Sheet Music
TAP Music - Specializing in brass music and recordings
Trumpet Websites and Blogs
International Trumpet Guild - If you enjoy trumpet, you should be a member!
Trumpet Herald - A great resource, but don't believe EVERYTHING you read. It is just one source.
Doctor Valve - Trumpet repair
Charlie's Brass Works (Charlie Melk) - Trumpet repair and customization
Music Theory, Ear Training, and Practice Tools
Theta Music Trainer - Ear training games