This Digital Alchemy article describes how you can use a plus sign (+) to add a sub-email address to any gmail address....
" Gmail has an interesting quirk where you can add a plus sign (+) after your Gmail address, and it'll still get to your inbox. It's called plus-addressing, and it essentially gives you an unlimited number of e-mail addresses to play with."
" Example: If your address is firstname.lastname@example.org, you could use
email@example.com for nytimes.com
firstname.lastname@example.org for freestuff.com
Then you can tell which site has given your e-mail address to spammers, and automatically send them to the trash. "