I use the Griffin stylus. I think they can be found for around $14.99 now. I got it when they were first released, about a year ago. I hadn't used it much until I started playing Draw Something. It make it a lot more fun. I'm sure there is a more accurate stylus out there, but the game doesn't require much precision.
Amato27 is my username if you want to play/laugh at my drawing skills 🙂