Perhaps I am boring, but I have always been a fan of the box standard Cumulus cloud.
I used to spend hours as a kid in summer holidays, lying on the ground and looking up at the clouds trying to make shapes out of them. After a few bouts of nasty sunburn, I learnt to do it from inside! A rabbit and a WV Beetle car where what I mostly saw, but then again my imagination probably wan't too good then!.

More for old times sake, here is one I found on the web. A rabbit and Road Runner!