Random Addresses:

US Street Addresses

Use this tool as test data for an automated system or find your next pen pal by cold snail-mailing letter to a random address. If its not an actual address, the post office should return it back to sender.

It may just be fun to annoy your local post office by mailing letters to these locations. They'll have figure out that its an incorrect address and get it back to you. Then you can readdress it to some other fake random address.