Game Boy Map Builder
Game Boy Tile Designer, by Harry Mulder, is a graphical tiling application.
It reads GBR files from Game Boy Tile Designer and paints with the tiles there.
It exports to various assembly filetypes, binary, and a C array.
We're storing a copy of the most recent version: http://gbdev.gg8.se/files/tools/
The original website, for historical purposes is here: http://www.devrs.com/gb/hmgd/gbmb.html