I've always considered a pregnant woman's form very sexy, the shape that shows a woman's femininity and strength at the same time. Here's something to remember that shape for years to come, even long after the baby's out and all grown up: the Proudbody Pregnancy Belly Cast Kit:

A pregnancy belly cast, sometimes called a belly mask or belly mold, is a plaster cast made of an expecting mom's beautiful pregnant form. Pregnancy is a very special, yet fleeting, time in a woman's life and memories quickly fade. Photos only capture a flat 2-dimensional image, but a pregnancy belly cast captures the exciting transformation a mom undergoes during pregnancy in a full 3 dimensions! A pregnancy belly cast enables a mom to forever remember how she looked during her pregnancy and the special nine months she shared with her growing baby. As one mom aptly put it, "It is a really cool way of capturing your pregnant body. You can show your child later that this is what mom looked like when you were inside!".

I'm definitely having this, probably when I'm on my 7th or 8th month when my belly's real big (Ideally it's done about 4-6 weeks before the due date). I originally thought of asking an artist friend make me a cast, but it looks like this kit is easy enough for even a novice, and, at less than $35, it's cheap enough to do several times. Come to think of it, I probably should have one done for every trimester at least.
Have a look at this gallery of pregnancy casts for more iideas on what other creative things you can do with your cast.