Question about hard drive space being filled up with "other"

So I have a 80g hard drive for my macbook pro. I basically use this computer for school work and music. When I try and sync my iphone is says everytime "cannot backup not enough disk space" I looked at what my hard drive is being used for about 8g of music and everything, then it shows I have 69.45g of "other" How can I figure out what this is being used for and delete it?