I bought an R4DS from gamebygame, and I got it less than 5 days later. I know R4DS won't receive more firmware updates, but it still has incredible compatibility and home brew capabilities. For $10 + no shipping, you can't beat it.
Currently on my R4DS, I have GameBoy Color, SNES, some videos, some music, and DSHobro's Internet browser.

Also, does anyone know if there are any games yet that R4DS can't play? The only one I knew of was Grand Theft Auto Chinatown Wars, but they patched it to work with R4DS.