I liked the "Chrome to Phone" extension that pushes any website you're currently viewing out in your browser to your Android device. Great when you need to test something on your phone or when you want to send yourself driving directions.
Also "Personal Block List" that keeps certain crapy websites from always showing up in my google search results. I HATE spammy sites that are just aggregate info scrapped from actual message boards. They always show up when searching for a solution to a technical problem. Once you add a site to your block list, like bigresource.com or devcomments.com, they never show up in my search results again!
I use "Auto Refresh Plus" every day because my the Plesk interface for our main server auto logs you out after 30 minutes and you can't update the setting. Auto Refresh lets me set my browser tab to refresh every 15 minutes to keep me logged in
I also have Ad Block Plus.
Oh, and pixlr.com has an extension called grabber which is great for taking screenshots/crops. You can select an area of the screen to copy and either save it to your computer, clipboard, or open up in the pixlr.com editor to mark up.