Designed for both Xbox 360 and the original Xbox, Kontrolfreak is a small plastic attachment that gives you better grip on the analog sticks on your controllers. It's essentially two wings that ensures your thumbs don't slide off and go flying, which honestly hasn't been a problem for us as far as we can remember. But we don't really go ape shit when we play games, despite what Kotaku says.
The price is 2 for $9.95 (enough for one controller), and will be available around late April or May.
Product Page [Kontrol Freak]