Hmmm.... *Goes hunting*
This site is good for jazz chords and scales. It has a chord and scale generator with every scale know.
www.apassion4jazz.net
With jazz chords, I dont know how much knowledge you have with chords etc. I guess you can pick some chords and experiment with how they sound together. An easy piece to experiment with could be Herbie Hancock's "Watermellon Man." It uses 3 chords - F7, Bflat 7 and C7. Perhaps experiment with those three. Im guessing this is what u are wanting to do
Has some good stuff in pdf and stuff
http://www.8notes.com/jazz/This site is good from memory, its been a while
http://www.mfiles.co.uk/index.htmhttp://scriptorium.lib.duke.edu/sheetmusic/There are a few there. If i find anymore then ill post them up. Jazz Fake Books are also another option, cept I dont know of any that exist online legally. This ain't the place for illegal stuff either.
As for free mp3s, thats tough.. Some musicians put a couple up on their personal websites. Just google for them I guess.
My favourite piece...hmm...thats really tough because I like a lot of different music styles. Rhapsody In Blue would probably have to be at the top of the list. Never get tired of it.