But what on earth are you going to choose as a theme? Most people fall into two categories at this point, those who have too many ideas, and those who have none!
So here are a few great ideas and suggested costume ideas to match, to narrow your choices. And don't worry, there are plenty of online adult costume shops that stock these sorts of items.
Angels and Demons
Wands would be good, large costume wings will stand out, and a little (or large!) halo to wear on top of your head will just cap off the Angel fancy dress outfit.
The Retro Party
Retro fancy dress parties really open the door to lots of great costumes. You can go for the disco cowboy look, girls can dress up in 'go go girl' costumes (complete with knee high boots!), or you can go for the John Travolta look, with tight pants, tight shirt with lots of chest hair.
Or, just to be a little different, how about a roller girl costume? Turn up on skates to really get people's attention!
A 'P' Party
P is a great choice because there are lots of costumes that begin with P, such as Pirate costumes, Princess costumes, pimp, porn star(!) and more.
This odea gives people a good number of choices, and you will surely find a wide range of costumes at a party like this, some will be very creative!
Often younger kids in the same age group will all like the same show or movie, so Dora or Diego might be good ideas for costumes, or Harry Potter.
I hope these ideas give you a good place to start as you look for great ideas for your next fancy dress party.