Currently the MPIO ONE is the smallest PMP, sporting a one inch 65K color OLED screen. The player supports MP3, WMA, WMA DRM, and OGG audio formats. On the video side it only supports MP4, but the included software easily converts MPEG4, WMV, AVI, DivX, and XViD for playback. Additionally, the ONE can handle JPEG and TXT files.
MPIO has packed quite a few features in this tiny package including a high end Wolfson audio processor. Additionally they have filled the box with almost all of the accessories you need. Even though this player is priced at a premium it is definitely something you should consider.