This can be so much fun.  People always remember theme weddings when they attend them.  Pick a theme that fits the two of you.  Favorite music, movie, country, time period, anything that you both love can be made into a theme wedding.
There are country weddings, 1950s dinner, train car, showboat, casablanca, Gone with the Wind, Sports theme (some ballparks well let you get married there), holiday themed, medeival, beach, Mardi Grase, Rock N Roll, Gothic the ideas are unlimited...