If you use Chrome or Chromium (and I highly suggest you try them out if you don’t!) here are a couple extensions for Gmail that I discovered that I actually use a lot. Not ground-breaking or breathtaking, but very useful:

Gmail checker – shows if you have any new emails and how many, and also serves as a shortcut to Gmail (opens it in a new tab)

Send from Gmail – does exactly what it says, it just copies the address bar of whatever page you are on and opens up a small gmail window to compose mail with that address in the email. It’s great for tossing pages at friends!