I don't know if you just want earphpnes or headphones as well, but I just got these the other day and they are awesome. Best headphones I've ever used with the system, and they also come with a microphone to boot (and it's adjustable, so you can move it out of the way if you're playing a game that doesn't use it). I got mine at Circuit City the other day for only $15, which isn't that bad at all.
I'm partial to the Koss Plug as they fit very comfortably but am also considering
checking out these Hori phones made for the DS. Link for those are the Japanese ones, but I've seen them at Nintendo World Store & Target. WOuld be nice to have the volume dial for those Phoenix Wright Jam-Outs.