If you want an impact wrench, you might be better off considering just buying an electric one. I think those impact drivers use a lot of air, so you'd almost have to up-size your compressor just to accommodate that one tool.
I've got the Harbor Freight 1/2" electric impact wrench (mechanics type tool, probably not for woodworking) that they sell for about $40, and it works great. I've taken off some pretty big, stubborn fasteners with that thing.
I've heard that the oiled compressors last longer than the oil-less, but I'm not an expert on these things.
I have a Husky (Home Depot) brand compressor, 8 gallon, cast iron cylinder, oiler, that has worked well for me. I've even run a LVLP sprayer with it and it worked very well. For home-use, it's been a nice unit, and about $120 or so. (basically, the same one that Steve Neul linked to above.)
Last edited by pweller; 03-28-2014 at 03:47 PM.