[puls]

Check out plus addressing! Not part of any standard, but supported by Gmail and many other email providers.

http://gmailblog.blogspot.com/2008/03/2-hidden-ways-to-get-m...

[kin]

I've tried plus addressing. Some websites annoyingly don't accept them :(

[sib]

The plus sign has been a valid character in email addresses since 1982 (RFC 822). See page 8: http://www.faqs.org/rfcs/rfc822.html