I usually look through eBay for some older or classics. Have to sort through the showtunes and over priced things for cool pieces. Hal Leonard is pretty good for collections in their play alongs. Sheet music direct seems to be pretty good and inexpensive for individual songs. What online or other places do you all dig around for sheet music?
"Pierre" has transcribed a ton of old school soul and funk lines on his web site. (Are you on TB, Pierre?) There is also a ton of actual notation (not tab) being regularly submitted as PDFs in TB's Tablature and Notation subforum
Only would take exception to his Mustang Sally transcription (Pierre). Ed Friedland wrote 2 good articles about it in recent BP magazines- the actual bassline is much more dissonant than you would expect, and it helps create a unique push. EDIT: a great tip from those articles on transcription- put the track in a program such as Amazing Slow Downer- then put the track up a full octave, now the bassline is much easier to discern, being up an octave, and you can clearly hear each pitch, as though it is played on a standard guitar. It really helps on complex and deep lines!
I'm not sure this is the direction you are leaning, but imslp.org is a great source for classical music in the public domain. (Think Mozart, Bach, and the like....)
Diesel I've mentioned this before here at TB, but you could take a look at scribd.com; $9/month, first month free w/no obligation.