Now when Teemu 1.21 is released I can take a look at my sprite editor Stile. I changed the name to Brick Atelier which I think is better, since there already is sTile and Stile is a boring name. I had to redo some stuff since I lost the original Brick Atelier version, but nothing major (I hope) was lost. Just the Brick Atelier logo for info screen.
There are some stuff I want in next version (0.83), mainly some kind of contrast/brightness (maybe even color) adjusting for selected tiles and tile import from another .wst file. Those I guess are the main features.
I think SDL could be a wrong library for this kind of software, because it has been quite hard to do GUI stuff from scratch and I still don't have a portable file browser (using Windows browser inside SDL which is some kind of hack). I just don't know if the current features could be done with some external GUI (and maintain the speed).