Got, ostensibly for my wife, a Sandisk Sansa e250 2GB music player (not e250R, not c250!). Actually, I got a Creative Zen V Plus first, for US$40 less, but couldn't mount it, and libmtp couldn't see it, so took it back. I promptly installed Rockbox. It was distinctly ugly with the default theme, but given a third-party theme (e.g. "Sansa e200" from rockbox-theme.org), it's wonderful.
The great surprise was the completely programmable equalizer: I can tune it to match exactly the response of my ears, which suffer a sharp dropout around 3.9KHz. The only real problem happened when I turned on "clear backdrop", just to see what it was, and now can't read the menus to turn it off. I will probably need to hand-edit the config file. Also, the Doom plugin fails on startup. I wonder why there's no Tetris plug-in... One of the nice things about Sandisk players is the microSD slot allowing memory expansion; Rockbox supports that now. [Update: copied the "backdrop" line from the theme file to the config file, and all is OK now.][Update 2: thanks to sneakums: tetris is "rockblox" and Doom needs WAD files. BTW, that 3.9KHz dropout is called "4K dip" by pros. Rockbox needs a hearing test plugin.]