I usually listen to music in headphones and i seem to have a decent set of ears, so sound quality means a lot. One cannot beat the audio-technica ATH-AD700 for the money. I found mine for ~$115 and they are stunning. Huge, but with glorious sound.
In a different category are my etymotic ER4S's. In-ear, sound blocking, great sounding. More expensive. Check out http://www.etymotic.com/ for more details. Oh yeah, and give serious consideration to the ety.com cell phone headset while you're there. Best one i've tryed, and i've tryed a bunch. A steal for $40.
In yet a different category, for beater/on the train listening, i use "Skullcandy Buds Inked" for less than $20 at Target.