I have a good one I bought at sears. I believe it's a craftsman
branded one, but I can't find a link to the exact one right now, but it
has a large LCD display on it. I bought this one because I can set it
to 1/2", 1", and 1.5" depths, which I needed. My house uses mostly
plaster or plaster on top of drywall (for a total thickness of about an
inch) and it still works good if you pick the right setting.
I believe the one I have is very similiar to this one:
And my house uses armored cable, and since the armor is grounded it
doesn't detect the AC very good though.