For my son's 5th birthday, he really wanted a Star Wars theme party. Since we were having the party at a gym, I kept it simple with just a few basic items to carry the theme.
If it's true that invitations set the mood, these cards from the invitation boss were the perfect find. And, inserting my son's face for Luke's was the best gift of all. It's a little kitschy but so cute for the young ones.
Finally, the cake. Each year, it's a tradtion for my spouse and kids to select their birthday cakes from Birthday Cakes: Recipes and Memories from Celebrated Bakers. I got this book just before my daughter turned one, with the intention of using it for her birthday every year. The recipes have been an indispensable resource for all kinds of cakes for family and friends.
My son's favorite for the past few years has been Emily Luchetti's Grandmother's chocolate cake topped with Marion Cunningham's buttercream frosting. This year, buttercream was gray, which was fun to make for my crude interpretation of the Millennium Falcon.
A few more recipes from the cake book:
Grandmother's Chocolate Cake (another way)