Yesterday I bought a pair of Philips SHE9000 because I wanted to get rid of the stock ones and was quite disappointed. To describe the problem: there are bass only in the right speaker which is very uncomfortable.
So I'm looking for the best one I can bought for 30$ (25€). The SHE9000 were intra but it hurted my ears hours after taking them out which is not good at all.
You can also investigate a little bit,there are a lot of chinese brand that do earphones well,tho you cant go wrong with pistons.Just watch out,there are a lot of fakes out there!