Well, it depends on what you like. There are about a billion cardio videos that focus on all sorts of activities -- low-impact aerobics, step aerobics, intervals, latin dance, belly dance, kickboxing, tae bo, walking/marching in place, and on and on. There are videos I like but they might not match your style or preferences or abilities or current conditioning.
One thing I find helpful is to go to
www.collagevideo.com and just start browsing. The staff evaluates every video they sell, and customers post reviews too. You can also view film clips online. They carry nearly EVERYTHING that's sold through regular retail. So, you can see what titles or types strike your fancy and go from there.
Just an FYI, I think Kathy Smith is one of the best video instructors out there. Her routines are always well put together and she is a stickler for form and the latest in exercise research. She has a wide variety of styles so you can't go wrong with picking her if you like the type of workout.