Letter-sized paper outside North America is known as A4. Until you see A4 and US Letter pages side-by-side they seem pretty much the same. In reality, the A4 sheet is slightly more narrow and a touch longer.
In a document originally written in 1999 (that recently popped up on digg.com), Brian Forte goes into great detail on A4 vs. US Letter. Can't read enough about paper sizes? Try these: