Have you thought about belly dance? There are a lot of DVDs out there (and some threads about which ones are people's faves if you do a search) and it's really fun. One of my favorites. :)

Pilates, maybe? It's tough to master but a lot of the exercises are done sitting or lying down. It's great for toning but not really for weight loss...I alternate it with more cardio-ish workouts.

SavingServo: Ooh Belly dancing does sound fun!