Laying with their legs all sprawled out, we call that the splat. It is one of those positions that gives me the warm fuzzy feelings because it means they trust you enough to fully relax.
Now talking about funny positions. I have had two that will roll on their backs.
Turtle used to sleep on my lap, on his back, with his legs raised up in the air.
Another is Poptart. She loves to snuggle under your hand when in her snuggle bag. However, she also loves tummy rubs, and will roll over on her back, push herself under your hand, and try to get you to rub her tummy. She will completely relax and lay that way for a long time as long as you rub her tummy. I had her at the Milwaukee hedgehog show last year, in her snuggle bag, in the show room, and she was happily laying on her back getting a tummy rub.