There is a nice article Mike Guadango from DeFranco's Training Systems up on T-Nation.
Time to Up Your Pullups
I've got personal experience with Mike - he's trained me. His own pullup numbers are excellent and he's demonstrated an ability to improve other people's pullup totals.
The progression to a pullup if you can't do one is good, too, although it does require a bit of equipment (rings, a place to do horizontal rows, etc.)
It's also got a nice collection of pullup variations at the end - including band-resisted (a favorite of Pete the Fireman) and correctly-labeled one-handed pullups (often mistaken for one-arm pullups).
Open #17.5 Strategy - MobilityWOD
1 hour ago