The first thing landscape photographers check when they frame the shot is to make sure the horizon is level to prevent crooked shots. While you can try to adjust the shooter by estimating with your eye, the Camera Cube can help you be more precise.
Measuring 1 inch all around, this leveler attaches to any camera with a hotshoe. The three-way axis lets shutterbugs take straight snaps whether the camera is mounted vertically or horizontally on the tripod.
Some dSLRs such as the Nikon D700 have an onboard electronic leveler, too, though critics may say it won't be as accurate as a bubble-based one. For me, I'm not sure if the Camera Cube is worth the $15 indicated on Photojojo's Web site, so I'll stick to the free Advanced Bubble Level iPhone app.