Bookmark Backup
If your bookmarks are vital for you, this extension will automatically backup your bookmarks into a folder. You are able to backup into different folders based on the day of the week.

Check out Bookmark Backup

Forecastfox
With this little extension, your local weather forecast will be presented on your status bar. Forecastfox lets you customize everything, from the number of days to be forecasted, to the content of the tooltips. You can decide whether to see the labels, and you can decide what toolbar to place Forecastfox in. The options window is intuitive and makes it fast and easy to change any of the settings you’d like.

Check out Forecastfox

Web Developer
This one was recommended to me by Kris some time back. Adds a menu and toolbar to your browser with various web developer tools. Current tools include converting form POSTs to GETs, hiding images, outlining block level elements, disabling styles and many more.

Check out Web Developer