These are already some programs that use XTiles (and SDL, of course):

A "tile machine" with its own programming language
By Fernando Aires Castello

Roguelike under development
By Fernando Aires Castello

By the way, if you happen to make something cool using XTiles, even if it's just a simple demo or prototype, you can send it to me, if you like, and I'll show it as an example here in this page.

Thanks! :D