I watch lots of things! So you think you can dance - seeing the girls gives me motivation; futurama (I barely notice the time go by); or a number of other entertaining shows.
The best thing I've found, the most important thing ( I may be different since I work out at a home gym ) is to watch something that's going to keep you entertained for the duration of your workout.
The best thing for you to watch is whatever engages you the most! Be it talk shows, decorating, history, music videos, cartoons, or even a movie!