I must agree on this one .. some web forms are clever enough that they have State/Province field and offer 'ON' for the province of Ontario (where I am). But I have come across eCommerce implementations that insist that I supply an American State, so I usually leave it as 'AK' (Arkansas, I guess), the first one on the list.

Then, of course, the 'zip code' (we call it a 'postal code') field may insist on numbers (NNNNN[-NNNN]) when the Canadian standard is ANA NAN. In the U.K., it's a mix of letters and numbers (like London SE 4); and in Germany I lived in 'D-7400 Tuebingen'.

Don't Americans want people from outside their country to buy their stuff? ;)