Wow, I missed this thread. Question for you though. How many people shingling? Are you going to run a framing gun to replace your roof deck or nail down the existing sheathing? If you're just by yourself and you aren't doing anything with a framing gun, a cheap 4 gallon compressor 120psi compressor will do the trick. Try to get something oil lubricated as it will last longer. Unless you're really, really quick at shingling you won't be running out of air. You don't really need a shingling hatchet to shingle the entire roof when you have a compressor and gun at your disposal.
As far as roofing guns go, I recommend Hitachi NV45AE and the Max SuperRoofer. I've used every roofing gun there is out there and those are the best from all my years of experience and thousands upon thousands of squares I've pounded off.