My wife was doing something on a forum she frequents that required her to create a new account. In order to do that, she needed to use a different email address, so she created a new GMail account. Had I not been in the shower at the time, I would have saved her the effort with these two tips.

• Use +. If your email address is example@gmail.com, mail addressed to example+website@gmail.com gets delivered to you, too. Of course, you can use anything after the +. This is pretty awesome, because it gives you the option to make filtering very simple. The downside is that not all websites think + is a valid character in an email address. It really is, but that doesn’t mean all sites implement a proper check.
• Use . . Another option is to insert a . in your address. For example, instead of example@gmail.com, you can use e.xample@gmail.com. This has the advantage of passing any website’s validation check. The disadvantage is that there are only so many possible places that you can put the ., so you run out of options pretty quickly.

Not only are these tricks useful for pretending to have a different email address, but they’re great for filtering as I mentioned above. One common use I have is to automatically assign a label to a message based on what address it is sent to, which is much easier to filter for when the sender and subject are not known a priori. It can also be used to see if a site you registered an account on is selling addresses. Getting mail from anyone not jerks.com to example+jerksdotcom@gmail.com is a good sign that jerks.com is handing out your address (assuming that you haven’t published it somewhere on the jerks.com site).