It won't win any battery-efficiency awards, but if you've ever wanted to be able to "see through" your HTC EVO's home screen, then the free C-ThruFone live wallpaper is about as close to x-ray vision as you'll get without being a superhero.
It actually just uses the phone's rear camera to display what's behind the device, but it's still pretty cool. You can even double-tap an empty area on the screen to take a photo of whatever is being shown, which can speed up casual picture-taking since you don't have to wait for the camera app to launch.
It doesn't take pictures in the EVO's full resolution or automatically rotate a captured image, though, so I wouldn't recommend using it instead of an actual camera app (default or third-party) for every single photo opportunity that arises. But for taking quick shots and maybe just showing off a great live wallpaper when battery conservation isn't your top priority, C-ThruFone is worth checking out.