Greek costumes are pretty similar to Roman costumes and are often mixed up on websites that sell fancy dress, still unless you want to be very technical bout it, I am sure that it does not really matter if you are wearing a Roman or ancient Greek costume.
Most websites that I have looked at have pretty large selections of Greek costumes, with every variation on the theme including a greek goddess costume, Zeus costume, Greek warrior costume, to what I thought was really excellent, a Greek statue costume!
The History of the Greek Costume:
The toga, is probably what most people think of when they picture a Greek costume or that of Ancient Rome, it was probably first introduced by the Etruscan civilization, people of ancient Italy and Corsica. The Toga is basically a sash, usually about six meters long and is wrapped around the body and worn over a tunic. In Greek and Roman times, the toga would have been worn by men and would have been made of wool. These days you can find toga fancy dress costumes for both men and women.
A spin off from a Greek costume party and an excellent idea for a fancy dress theme would be a Toga party.
Toga parties has become popular in recent times, especially at colleges and universities in the USA, much of which could have come about from the film Animal House. Other reasons for toga and Greek costume parties popularity could be because of the myth of Greek and Roman debauchery, and love of women and fine wine.
A toga Greek costume is also pretty simple to make, you could even use bed linen. Unfortunately, these "togas" bear little resemblance to the actual Ancient Greek costume, as they are both flimsier and scantier, but it is important to remember that a fancy dress party is all about fun and does not have to be historically correct!
If you want to know how to make your own Toga Costume, I found this pretty cool demonstration video on how to make a toga costume:
Apart from Togas, other ideas for Greek costumes include a Hercules Costume, Aphrodite Costume, the Goddess of Love, Greek Goddess Costume, King Of Atlantis Costume, Zeus costume, official Spartan Costume from 300 or how about an ancient Greek Warrior Costume?
Where to buy your Greek Costumes:
If you are looking for a Greek costume with a difference, I did mention the cool Greek statue costume earlier on, I found it on Jokers' Masquerade fancy dress. Check out their selection of Greek Costumes, there were 65 products when I searched including a bunch of Greek goddess costumes and all the fancy dress ideas for Greek costumes listed above.
Greek Costumes on Amazon.co.uk