How much are you looking to spend?
In my garage there is one of these
http://www.google.com/products/catal...wBA#ps-sellers
Overkill for average stuff, but if your getting serious this will blast almost anything off. We had a craftsman impact and it kind of sucked so we replaced it with an IR impact
This is it. The craftsman impact lasted 1 year of 240 wrenching, which means 10 months of DSM wrenching and 1.5 years of suby wrenching.
It really doesn't take up as much space as you think, but if you dont want the thing pumping all the time, that little thing isnt gonna cut it for you. While Im working on the car (exhaust, engine mounts, trans bolts, so far this week) it keeps switching on fairly regularly and gets annoying when Im listening to music. If you only want to use it for lug nuts, that little guy will be fine. If you want to blast off rusty downpipe bolts, manifold bolts, etc... you might want to get something bigger because that thing will be working overtime.