Various Helpful Links:

Trumpet Sites/ Blogs
Brian McWhorter - Site of Brian McWhorter, maybe you recognize him from the Way of the Blade Videos...
Farnell Newton - I don't know Farnell personally, but he created the well known Jam of the Week Facebook Page, and makes some good music!
International Trumpet Guild - ITG's webpage
TrumpetChris - Website and blog of Chris Coletti
Trumpet Herald - A huge trumpet forum.  Beware, many hours can be wasted here instead of practicing!
Trumpet Journey - Stanley Curtis' site
Trumpet Master -  A large trumpet forum similar to Trumpet Herald
Trumpet Matters- Blog of Phil Collins, former Principal Trumpet of the Cincinnati Symphony

Musician Blogs
Art of Practicing - Website of piano player and author Madeline Bruser.  Her book is really, really good. 
JazzAdvice - JazzAdvice is a great resource if you are interested in jazz improvisation (jazz patterns, etudes, and articles).
Musicians Guide to Hustling - Seth Hanes has many guests on this blog regarding marketing, self-publishing, freelancing, and much more.

Auditions
Last Row Music 
Musical Chairs

Summer Festivals
This page may not contain all of them, but it is a great place to start.

Sheet Music Resources
Blank Sheet Music - Pretty self-explanatory, you can print your own staff paper.
Erik Veldkamp - This site has many free pdf downloads of etudes, concertos, arrangements, and etude books. 
Imslp - This site contains TONS of free sheet music (public domain) for all types of instrumentation. You can find parts to all Beethoven, Mahler, and Strauss, to name a few.  
MuseScore - A free music notation software.  Similar to Finale (maybe a little less user-friendly), but free!