What cool feature did you just finish programming / get working?

I just got the basics of a cell-based 2D world done (think Morrowind or Oblivion, but 2D). Next up I'll read these in during gameplay to create a seamless 2D world :D

EDIT2: Here's the first area of Super Metroid redone in my editor: http://i.imgur.com/O2cko.jpg

EDIT: Also, post screens if you can! Here's what my editor looks like so far: http://imgur.com/1jKKJ.png