What I've always done to clean my pipe is take warm water and some uncooked rice. Put some rice and water in your pipe, and shake vigorously. The rice should scrub against the inside of the pipe, getting it squeaky clean. Also, you can buy some nailpolish remover, it basically dissolves resin. I put my pipe in a glass of nailpolish remover for 5 minutes, and when I checked on it, the nailpolish remover turned from clear to yellow.

It obviously works very well, just make sure that you clean out your pipe really, really, really well (repeatedly filling it with warm water, shaking it, and emptying it out works wonders) if you use nailpolish remover. It'd probably kill you if you smoked it.