Tiled was designed as a generic map editor, so that game developers would spend less time building their editors and more time creating their games. That it also provides an alternative to proprietary editors like the one found in GameMaker is a nice plus. :-)
This is pretty much exactly what I was looking for, I'm wanting to make a Pokémon-ish map for my Indie Game Making Contest entry, but wanted to use GameMaker for the battling over RPGMaker. I fear I'm horribly under skilled for my vision, but hopefully it turns out okay, lol.