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Just as an aside, get the one with the 1/4" chuck, then buy the 1/4" to 1/4", 3/8" and 1/2" adapters. The 1/4" chuck is way better than would seem, and the boss ring on the 3/8" falls out pretty much instantly, meaning it won't hold sockets. Trust me, I've used all the DeWalt cordless impacts, the 1/4" punches way above it's weight.
Best bang-for-buck IMO is the DeWalt 18v 1/4". Especially if you already have the batteries, or easy access to some. Obviously a lighter duty impact. I prefer the 1/4" to the 3/8" because you can just buy the 1/4"-to-whatever adapters, as well as just replace the adapter if the ball/ring retainer wears out. (the socket retainers on the 3/8" are garbage).
thats a regular drill. not an impact driver this is what i use http://www.amazon.com/DEWALT-Bare-Tool-DC825B-18-Volt-Cordless/dp/B002RT7K4Q
its a very versitle impact driver. just be careful when driving larger things like 3/4 lags. i snapped off one of my bits in the chuck. it twisted that 1/4 adapter like a twizzler