I liked the ones they had at gamestop...not for looks but because it adds just the right amount to the controller mass wise. Not to mention it is more comfortable for longer sessions. I bought a black one and a red one from gamestop for $10 and I've really been pleased with them. (They were pretty durable and not thin.)
I went back to buy two more and all they had left was a pink one. (I know say what you will but I can't do it!) I checked the other Gamestops in town and they were all out. Their website isn't carrying them either. I think the ones they do have are the MADCATZ brand.