My take on your situation is that you're looking for a pair of good headphones for general use? If so, just buy that - good headphones.
Personally, I'd rather buy an easy-to-drive headphones which don't require an amp to sound good. Some brands that some to mind are Audio-Technica, Ultrasone and Grado. Most of their headphones, arguably, don't neccessarily NEED an amp to sound good. Headphones are by far the most influential component in your audio set-up - if you don't NEED, or don't want
, an amp for your headphones to sound good, don't get one, it'll just be unnecessary and you wouldn't notice a whole lot of difference anyway.
Keep in mind, I am assuming you have quality sound source; (1) Quality music recordings, not just random music poorly ripped from a CD at something like 128kbps, or worse, downloaded pirated music with serious distortions and weird sounds added. Headphones at $300 WILL reveal the bad, to an extent, in your music recordings. and (2) Decent quality DAC, which an iPod has, or a good soundcard, or even better an external USB DAC (digital to analog converter), but you need an amp with an external DAC.
What uses are you intending for your headphones? Games/Music/Movies/all of the above? Which uses are more important? If you have these details more people are able to recommend specific headphone models.