scds2 - great features, gba/snes emulation, exclusive homebrew, great support, video player, pdf viewer, fuzzy cheat finder, in-game menu options, etc
ievo - dsi-mode, avg homebrew support, not much exclusive homebrew content yet, in-game menu options, above avg support but fixes for stuff like homebrew have yet to come.
ak2i - crap build quality but supported by akaio
ak2.1 - better build, akaio support, dsl/dsp only
ismart mm - iplayer oem released by ismartds and supported by supercard. pretty good support, nice features, in-game menu options, and well constructed. gba emu and video player as well.
r4ds (the original, sells for about $4-6). supported by the wood firmware, only works on dsl/dsp.
r4i gold (by the .cn team), runs on dsi/3ds and has wood firmware support
probably more but i'm tired and its 3am so thats all i got for you.