Mongolian formal wear, always fun (6-12th century, don't know about the present).
A fully Victorian Masque... or even neo-Victorian is fairly standard, but can have quite the effect.
Greek, although make sure people who choose to wear togas wear Actual togas, not bedsheets.
Colonial era Indian/British crossover... slightly harder to pull off...
Native American garb, with appropriately simple food
Aladdin-esque middle eastern theme
There's a few, just sticking to existing times and cultures. Add in fantastic elements to any of these and you can turn them into any number of things.
