Ahoy.
I've been trying to do some more ab workouts and stretching since my knees have been killing me lately.
This might be a little dorky, but I found this video on youtube and it included a couple of ab exercises that I've never heard of before. So, if you're just dying to try some new ab workouts....well, be my guest!!! I liked this little video, and I hope you do too.

http://www.youtube.com/watch?v=Y9Ws7DpDoOY