I am fascinated with the Zigview-R ($280, street), a color LCD screen you can rotate to view what is in the viewfinder. The Zigview-R is the perfect thing for me, since I am short and often have to shoot blind, holding the camera high into a crowd to get the shot.
For shooting low, a right-angle viewfinder comes in handy. Hoodman has a Right Angle View Finder that’s compatible with most of the major DSLRs ($130, direct). If you haven’t ever been on your belly trying to get your eye down low enough to look through the viewfinder, you haven’t lived life to the extremes.