I picked up one of the black Prince Lionheart SeatSavers last night. It was around 20 buck at Toys R Us. It looks a lot better than the towel I was using before, and gives more reliable protection against little feet on the front of the seat, too.
It's available in several colors.
I think it will do a better job of protecting the seat for two reasons:
1. It's rubber, so things won't soak through (important during potty training

).
2. The rubber is better at spreading/distributing pressure than a towel.
It looks pretty good doing it, too.
We'll be testing it on a ride up to Cambria (northern part of Southern California coast) this weekend. When we get back, I'll probably get one for the wife's car, too.