One of the most popular dinner party themes is ethnic food. If you've got guests with finicky palates, stick with cultures whose foods are more mainstream (at least by Americans standards), such as Italian, Mexican or Chinese. Adventurous diners can sample Thai, Ethiopian, Indian or Japanese cuisine.
Decorations can be simple -- a red-and-white checked tablecloth topped with a candle in an old Chianti bottle for an Italian theme; paper lanterns and a big bowl of fortune cookies for a Chinese theme; figurines of elephants (sacred to the Thai people) and banana-leaf placemats for a Thai theme.
Play music from those cultures to add to the ambience; just make sure the volume is set on the low side.