Organize your inbox by placing "+" in your email address. Any emails sent to the following email address:
email@example.com will be recieved by
firstname.lastname@example.org because gmail ignores the "+" and anything after it. However, this "+webapps" is searchable in gmail.
Using this, it is possible to set up filters to automatically sort emails based on the address that they are received at. So, you may give websites that will be using your email address primarily for notifications
email@example.com while you give shopping websites
firstname.lastname@example.org and have them automatically sorted into the appropriate labels.
This saves both the time it would take to create multiple filters for multiple sites (e.g. one for Amazon, one for Barnes and Noble, one for Woot that all apply the same label to your email) and is a more reliable method of filtering email than using the sender or the subject.