Fiji gets my vote! They all wore a garment called a "sulu" which resembles a skirt -- because it IS a skirt -- except for the flag-bearer who rocked an even more awesome ensemble involving tapa cloth, some kind of vegetable matter, and bare feet (apropos because he competes in judo).

Who was your favorite Olympic costume?

Mexico!

While teams from most countries wore the same uniform, the Mexicans donned different outfits with colorful variations of a unifying design. 

An "awesome riot of color":

Nigeria's uniform was pretty dope:

Yes, the Nigerian outfits were great.

Overall the 2012 Olympics opening ceremonies were spectacular.

I also enjoyed the German pastels even though I shouldn't because they're so flashy:

Compare with Canada, which didn't even try this year: