I would go with the SR80i and a few tweaks posted http://www.head-fi.org/forum/thread/508459/sr60-mod <here. iPod should be able to power any grado just fine. If you want to upgrade later I would skip the 125i, 225i, and get the 325is. I prefer them over the SR225i.
It offers about the same clarity as the 325 and RS2 and can sound pretty darn close with a few simple mods. That's my take on it.