My youngest is a Scientist. He invents things constantly, loved magic tricks, gag gifts and practical jokes, but most of all he loves all things science. For Christmas last year, he asked for chemicals. (For the record buying chemicals for a 7rd old turning 8 is not something that is accomplished easily.)
For his birthday, he decided on a Scientist theme. This worked perfectly for me as I managed to contact the local high school Science Teacher who welcomed us into her Grade 12 science lab on a Saturday for an hours worth of science experiments - bunsen burners and exploding Gummi Bears included!
I may have surprised him with his birthday party, but he had a lot of input into his birthday cake. He picked the most "Sciencey" word he could think of for around the side of the cake.