Mars.
Since the first image I saw from Mars Pathfinder, 11 years ago, I have been totally and utterly infatuated with Mars.
I have looked at every single one of the more than 250,000 images sent back by the Mars Exploration Rovers.
I have made mosaics, animations, lectures, 3d models, and a fairly successful forum. I've done podcast like Q'n'A's, talks to astronomy societies, live uStream casts. I wake up, I check for pictures from Mars. When I go to bed, I check for pictures, just in case. When Phoenix landed, I had 90 minutes sleep in 40 hours, just to make sure I didn't miss a thing.
It's a barren, beautiful, fascinating, enticing, dramatic, inviting, exciting world, and we've barely started exploring it.
Doug