One of my favorite birthday party themes that we've done for my daughter is her fairy party. I designed a cute fairy invitation, with a pink watercolor background and silhouettes:
For the cake, I bought the delicious chocolate round cake from Costco and just spruced it up with a bunch of sprinkles and a topper I designed to coordinate with the theme. We placed it on a dessert table decorated with a banner and tissue paper pom-poms. I purchased fairy wings, tutus, and wands for the girls to wear at the party and take home as favors (comment below if you want the source - great prices!). It was fun, cute, and a great memory for my daughter!