Ingersoll-Rand 2135TI 1/2' Impact Wrench Titanium
this is one of the best out right now. ive used one myself and they are kick ass. its really light and i think out-powers almost all on the market of 1/2 impacts.
Ingersoll-Rand 231C General Duty Impact Wrench
this one has plenty of power at a damn good price for the quality and can break loose just about anything you might come across. its pretty heavy but will last forever and can withstand some serious abuse. like i said earlier, i work with a guy that had this exact gun for over 20 years and still works perfect and has just as much power as new. (i think he had to change one o-ring but thats it)
sorry, im sure i seem like a tool salesman by now

tools are just a big part of my job and have been for years. im on the tool truck that comes by my work every week and he always tells me about new products and what he thinks about everything.
:edit: this is the one i use now. i have had it for over a year now and still kicks ass and is really light. i haven't come across one bolt that i couldn't get off with this gun. it claims to have a 1000 ft lbs. the book that came with it says 1200. im sure its not either one of those but its not far off.i think its as light as the titanium at almost half the price. i would buy one again if i had to.
ok! im done talking about tools! hope i helped a little. if you have anymore questions lmk.