I just found the picture of the onesies we made for my teeny tiny niece, Ellie at the freezer paper party we had. I mentioned them way back here, and again here.
Almost all of these were made using freezer paper stencils, so they might give you some ideas. The four on the bottom are my favorite. That kitty was so unusual and mod. I would never have come up with such a cool design. (Good job, Charis!) The seahorse on the left was inspired by an Eric Carle illustration. I made one new one, but the angle makes it hard to see. It's way up at the top, second from the left. A dandelion. (click the picture for a bigger view)
I highly suggest hosting a freezer paper onesie party for a mommy-to-be. It was a huge blast.