For that kind of money, if you don't mind looking like a dork, there are two phones which I personally like alot.
#1
'Eggos' are agreed to be one of the best deals under 100$ *and* can be driven very well from any portable player. Walkman.. minidisc player.. CD player.. they can all drive these earphones up very high.
#2
The Grado SR-80s.. are widely regarded as some of the best (In terms of sound quality) under the 100$ mark. After a period of break in (Maybe let 'em play your favorite music for about 80 hours and they'll sound *much* better) they sound awesome. The sound at first might disapoint you but after break in they are wonderful. The same is true for the Eggos to a lesser extent. Good Bass and trebble.
You can't go wrong with either one.
If you want something less dorky, here's my short list.
#1 Sony MDR-888 LP earbud (sounds great. A little short on the bass though.) Runs 50$
#2 Koss Porta Pros (Will go up to ear splitting levels on a gameboy, slammin bass) 50$
#3 Maybe the Sony EX-71s. They're built for heavy bass and sound decent. Not as musical as the 888's.
I'd reccomend the top two over anything on my shortlist, though.