I've owned a pair of Grado SR 80i for about 8 months and I love them. At first I wasn't too convinced, but after a few simple mods and hours of burn in they've been amazing.
I want to upgrade to a better headphone, and since I like the Grado sound signature, I've considered Grados (although I'm open to other suggestions). I listen mostly to rock and metal, and to some jazz, classical and electronic music and my sources are a Macbook and an iPod (unamped). I've done some research in the forums, and I've read that an upgrade to SR-225i is not that much of a difference and that the SR-325i is too bright and fatiguing. Most people recommend the HF-2 (although apparently you can't find them anywhere), the RS-2/RS-1 and the Alessandro MS-2. I was also wondering if an upgrade is really worth it considering my sources (some people say that it's pointless). I would really appreciate your suggestions.