I don't know if this was discussed already, but I was thinking about hacks for the GBA versions of Donkey Kong Country 1 & 2 that do fixes for graphics and some of the music. In the graphics department, palette fixes that instead use the palettes from the SNES games; also, animation fixes for some sprites that are either too slow and/or missing frames (Diddy's idle animation comes to mind). In the music department, some minor fixes for several songs that range from missing some notes (Jungle Hijinxs, for example) or have a few notes too many (Ice Cave Chant, for example), to screwing up great parts of the song (Forest Frenzy as a minor offender, Tree Top Rock as a major offender); apparently the composer of the GBA port did not pay enough attention to the soundtrack when recreating it for GBA from scratch. Also, correcting track names from the sound tests (Simian Segue to DK Island Swing; Kannon's Klaim to Mining Melancholy).
A fix could also be made for Donkey Kong Country 3, but only in the graphics department (colors and animations; Kiddy's sitting animation looks a bit off, for example).