Game Boy Advance SP-style personal media player, available for around $50 from DealExtreme (in silver or black). Perfect for those of you who want a GBA form factor without having to involve actual GBA games.
The device has 2GB of flash memory, can play MP3/WMV audio and a few video formats, and has both an external speaker and a microphone (with voice recording capability). But most importantly, it looks like a Game Boy Advance SP, for pretty much no reason.
See also: iGame, YD-965 Dot Matrix, the cutting edge of Nintendo DS clones, Nintando Version 2.0 handheld