What do you recommend for on-ear headphones for AAC/MP3 files?

I'm looking to buy some portable on-ear headphones that I can easily slip inside my backpack or computer bag. The key is that most of my music is 256 kbps AAC files. I'm looking for some headphones that will make them sound good, but not so good that they start sounding tinny and crappy. Preferably under $100, maybe under $150. I'm mulling over maybe just getting a 160 gig iPod Classic and putting as much of my music as possible on it as lossless files, but that's a few hundred bucks, and then getting decent headphones that can play the music nicely. It's pretty hard these days to sample headphones since you can't try the sound of what's at Amazon and Best Buy is devoted to Beats. Any thoughts?