I've used povray for creating objects I've used in mapping, and to create maps as well. It is extremely powerful, but great and easy for mathematical/scripted/repetitive shapes.
I made this paddlewheel for a top down paddlewheeler map:
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8E3_paddle_wheel_double_overlap_wood_rma.png [ 366.04 KiB | Viewed 2195 times ]
Palm trees (I was able to randomize a few dozen in size and leaf orientation so they wouldn't repeat when used):
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palm2_RMA.png [ 241.68 KiB | Viewed 2195 times ]
Asteroids from a videogame:
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rock_render1.gif [ 164.5 KiB | Viewed 2195 times ]
I've also used POVRay to render height-fields of objects,shapes and entire maps, like this one:
-Rob A>