Some camera have a built in electronic leveling feature like the Canon 7D. This is helpful trying to get your camera's horizon straight, especially when it's too dark to view the little bubble on your tripod. Also helpful to know when your Steadicam is flying straight. Here's a clever little 3 axis electronic leveling device that replaces your cameras viewfinder, or you can remove it to place on to the hot shoe. The little green lights let you know if you're off axis. It is quite pricey for something you can probably find an analog hot shoe level for $1.00, but if having a level on board your camera without adding bulk (or ugliness), here's an option. Appears to be available for Sony, Nikon, Canon, and more. Found below (click here).
Electronic Level DSLR ViewFinder Eyepiece