Articulated, snap together, Mars Rover! No screws, glue, or support structure needed (although some glue in a few places wouldn't hurt). All the parts can be posed, turned, twisted. The wheels turn and the legs even pivot like the real thing to go over obstacles! Unfortunately, it is not autonomous.

http://en.wikipedia.org/wiki/Mars_Exploration_Rover

2011-07-19 Update: V3 fixes a problem with plate 5 that was causing some pieces to be too close together and get merged, makes the axel holes in the body a little tighter, half the panels in the plates have been flipped so that the shiny side of all pieces printed on a HBP can be on top, I made the dimples on the panel tabs larger so they hold together better, and I also added squares to the panels to make them look more like solar panels.

2011-07-16 Update: I uploaded a new version of everything with a few changes like dimpled tabs for the solar panels (thanks to gpvillamil) and slightly larger holes to make it easier to snap bolts into. I also added a variable to the openscad script called tolerance that you can use to make those holes slightly larger. If you print the tolerance_test.stl you can use it to help find the right tolerance for your printer. The holes range from a tolerance value of 0.0 to 0.6 in 0.1 increments and the files I uploaded are 0.2

You're definitely going to need a stepstruder to print this. There's lots of little tall/narrow bits.

The tolerances are really tight and a few parts might require some drilling/sanding/or a lot of force to get them to snap together. You'll probably break a few bolts trying to get them to snap together, don't worry they're small and you can print new ones quickly. You can always play with the measurements in the openscad file to suit your printer. Also, the solar panels aren't very secure and tend to fall apart and could use a little work to make them snap together better.

Take a look at the "layout" part in the openscad script to help you figure out how the parts go together.

I suggest printing plate 1 in yellow plastic, plates 2, 3, and 4 in black plastic, and plate 5 in white.

The zip file contains all the individual stl files.

20 models 42 total parts

BOM: 1 body 1 panel_center 1 panel_back 2 panel_side_back 2 panel_side_front 6 wheel 2 axel_front 2 axel_back 12 bolt 2 arm 1 arm_sensor 1 target 1 antenna_uhf 1 antenna_low 1 antenna_high_bottom 1 antenna_high_top 1 camera_bottom 1 camera_top 2 camera_top_side 1 camera