For 6 months I have been using this soft vinyl one that fits perfectly: RocketFish HTC Evo 4G Soft Shell Case (RF-WR542). I had to slice off a mm of vinyl from the port at bottom for USB plug to fit, also had to do surgery w/ razor blade to make room for earphone. The camera slot is *perfect* for the 4.2 because it just clears the camera enough to avoid obscuring it, but provides an overhang that offers a little protection. There is a small hole at top for phone antenna, which of course the 4.2 doesn't need. But this actually makes a great place to attach a hand strap making it much easier to carry around safely; I highly recommend.
When not in use I keep it (including shell case) inside CaseLogic's 5.75" x 3.5" x 1" neoprene camera case, which fits easily in pants pocket, though with little room for much else.
I find both these cases to work perfectly, although some initial surgery required for the shell case. I change batteries fairly often, and it is pretty easy to pop off the shell case before popping open (with paper clip) the back of the device.