Considering this is one of the biggest releases this year and of all time for Xbox 360 Amazon cant even be bothered to tell us the difference between the 3 copies. The UK Amazon isn't even selling the limited edition 360 but Amazon.com does?
As far as I can see, there's not much in any of them;
Standard: No extras at all, so 2nd hand buyers won't miss out on DLC codes, unlike Forza4 customers.
Limited: Sounds like you get a little COG flag, some photos and a "last will", none of which anyone seems very impressed with, so to me it seems that the only thing worth paying extra for in this set is the metal COG trophy thing....BUT....unless you just want it as an ornament, then you need to buy this set new, as engraved on each trophy is a unique code to download an extra character in online play, so anyone buying this second hand will probably find that the code has already been used and is void.
Steel edition: I really can't find anything extra in this set at all. I find it hard to believe you pay all that extra for a pretty box, but that seems to be the case, if you'll excuse the pun.