Montreal postal codes -- or Montreal zip codes, a term rarely used in these parts -- are easy to find with this Canada Post Postal Code Finder. Just type in the address and voilà! It also finds postal codes anywhere in Canada.
Find a United States Zip Code
The United States Postal Service offers an online zip code search tool similar to Canada Post.
Find International Zip Codes
Check out Frank's Compulsive Guide to Postal Addresses, courtesy of Columbia University. From Netherlands Antilles to Liberia, Liechtenstein to Brunei Darussalam, author Frank da Cruz has got every corner of the globe covered, he's obsessed! He even explains what format addresses should be written in to conform to a country's postal standards if necessary. An incredibly useful tool.