World Artist looked good but is no longer developed. However, the source was released.
I actually purchased World Artist way back when and got the beginnings of a game out of it. Binary Phoenix must have abandoned it right around then. Just today, I visited the site and saw the source was available.
I've used Mappy and Tile Studio. I've tried every 2d map editor I can find. I've actually gotten a few working projects out of Tile Studio, although I never completed any of them.
Among the features I consider must-haves are undo/redo, the ability to paint collision data onto tiles, a tileset importer that allows for tilesets that may have borders and/or space between the tiles, an intuitive copy/paste setup (one of the worst features of Tile Studio is its copy/paste functionality, in my opinion), zooming and scrolling of the map, especially while painting (when the brush hits the edge, the map should scroll), and some sort of usable exporting function, XML being just fine in my opinion.
TuDee is very close. I think the lack of a usable base importer is ludicrous, and there are a few other issues, but it looks like a quality program, overall. I just don't want to buy any more abandonware, the way I did with World Artist.
SpaceAce