Jillian Micheal's workouts seem popular. The 30 Day Shred has 3 20-30 minute workouts so you don't have to workout for hours.
If you have a blockbuster or netflix account you can rent some out and see what you might like. netflix also has alot of workouts on 'watch now' so you don't need to even wait for them in the mail. The library might be worth checking out also.
http://www.exercisetv.tv/ has a few full length workouts if you browse around and lots of clips of other workouts so you can see what instructor you might like.