I'm building my GB dev environment. So far I have GB Tile and Map builders for backgrounds and GBDK for code. However I have yet to see good editor for sprites. Of course since I am using GBDK, it should export to format usable by it (preferably C sources, just like tile/map builder). Also ability to life display animation is good as well.
I've also looked everywhere for good graphic tools for Gameboy. This might not be exactly what you are looking for but it can convert PNG to Gameboy graphics (z80-source, GBDK C-source or binary) so you can use your favourite image editor for drawing. You should be able to do sprites as well.
Pic2Tiles
http://gbdev.gg8.se/forums/viewtopic.php?id=155