WOW! Thanks for asking, though it is a bit of a reply.
Right now I'm an ARC Trooper (Advanced Recon Commando:
http://www.starwars.com/databank/organization/arctroopers/?id=eu), however when I started on my costume before Episode 3 (E3) came out, I modelled it after Commander Bly (at the time there was very little in pictures and such until the DVD of the movie came out):
http://www.starwars.com/databank/character/commanderbly/index.html
The reason for the difference is that I don't have all the parts to the costume as of yet finished and I have to change my paint scheme on my chest to match what was seen in Episode 3 exactly.
Of late though, there are hardly any Episode 2 or Clone Wars (the cartoon which occurs between E2 & E3) in the 501st so I might just wait until I make another costume in the future and do that one to the Bly spec.