I love Pilates, and like stacie said, you really notice if you stop doing it. When I do Pilates regularly I feel much, much better- in general and on the bike. It's a great addition to any fitness plan.

I've not seen Pilates specifically for cyclists but there is a DVD called Yoga for Cyclists. I've seen it on Amazon and in the Terry catalog, but I've never tried it so can't comment any further.