Did you ever had to register into your webapp with multiple accounts to check if it's all ok? Do you have multiple e-mail accounts for this?
Yes? This tip is for you...
Pretend that your e-mail address is email@example.com. You can use your GMail address like this:
firstname.lastname@example.org email@example.com firstname.lastname@example.org email@example.com ...
Sky is the limit (I guess).