Chocolate happens to be one of my favorite topics!
You could do:
Truffles, mousse, cheesecake (could be all chocolate or chocolate chip or white/dark choclate swirl), brownies, mocha cigars, chocolate creme brulee, a shortbread tart filled with ganache and topped with raspberries.......I could go on, but I won't. Have fun, play around with ideas and if I were you, I'd visit
www.mrchocolate.com for inspiration. Let us know how the party goes!