I love Peeps, and a friend of mine really wanted me to make a Peep cake that included actual Peeps (as opposed to a cake that looks like a Peep). I decided to do a two-layer yellow cake with seven-minute frosting... I put Peep bunnies between the two layers and around the outside, and did a starburst-type pattern with Peep chicks on top.
I was really happy with how it turned out! If you want to make one, I have all the details at Eat. Swim. Shop.