The Official Gmail Blog points out two little known ways you can modify Gmail addresses and still get your mail. That means you could hand out variations on your address to different people, then use Filters to handle mail coming from different sources:
Append a plus (“+”) sign and any combination of words or numbers after your email address. For example, if your name was email@example.com, you could send mail to firstname.lastname@example.org or email@example.com.
Insert one or several dots (“.”) anywhere in your email address. Gmail doesn’t recognize periods as characters in addresses — we just ignore them.
[Via Official Gmail Blog: 2 hidden ways to get more from your Gmail address.]