Here's the latest Tile map editor im trying out for the GBC maps and tiles, its called Tilebuddy and its made by Gamebrains. Here are the main pannels.
This is the main screen were you assemble the maps. To edit the tiles click on VIEW>TILES to get the tile editor.
When you make a map with it and save, you end up with 3 files, 1 contains the map, 1 contains the background tiles and one the forground tiles.