Matt Thorson (Jumper, RunMan: Race Around the World) has released a general-purpose 2D tile editor called Ogmo Editor. It’s an Adobe® AIRâ„¢ application that works in Windows, OSX, and Unix, and exports tilemaps as an XML file or as a PNG. There’s a tutorial available to help you get started. Ogmo Editor is donationware.
Last year, Matt also released Grandma, a free platform engine for Game Maker that’s based on his Jumper 3 code. I’ll definitely be checking that one out at some point. Thanks, man!