So last night I made the crappiest sprite editor ever, but I'll rewrite it tonight... here's the BASIC concept (bad pun)
For the sprite drawing-
Start with an all 0 8x8 sprite
Using the arrows and F1-F4 you can change the pixel you have selected (or 8x8 area in this case) F1 being white, F4 being black, and F2 and F3 being Light and Dark grey
You can then save the sprite to wherever you want on the sprite sheet.
For map Editing-
Start with an all 0 8x12 map
Using the arrows you can move around the map
Press 2nd to change to the spritesheet and select your sprite
Press 2nd again to put that sprite into the map
Press ALPHA to put the last called sprite in the map at the current spot
Saves to [A] for easy profram inputting
Last night I made it 3lvGS, but tonight I'll make it 4lvGS