Sanyo thinks that including built-in memory in MP3 players is passé, so that's why its DMP-M400SD requires you to purchase your own SD cards on which to store your music. While this probably helps keep costs down and does give you the most flexibility and sovereignty over how you use your MP3 player, it does give the DMP-M400SD a sort of "also ran" feel.
The player supports MP3 and WMA files, DRM'd or not, and accepts SD cards up to 2GB in size. It'll play music for 12 hours on a single AAA battery, and its backlit LCD handily displays all the pertinent information.
So if all you want is a simple, bare bones MP3 player and don't having a pocket full of SD cards, the $60 DMP-M400SD might not be a bad idea. That is, so long as you're willing to wait until August when it's released in Japan.
Sanyo DMP-M400SD MP3 player [Fareastgizmos.com]
Sanyo (in Japanese)