Datanyze is probably my most used extension at work. One click and I can see all the technology a website is using. It's not the most reliable system in the world but it gives me a heads up of what I'm looking at. It also frequently has a list (including emails) of some of the people who work there. Score one for the home team.
Intricately Right now I'm using the free trial version but it's one of the best apps out there if you want to know what a company is paying in terms of IP services like Hosting and CDN. If it's something you think you'd be interested in you should totally use my link to sign up. It gives me a week or so of free premium service. Dooooo it.
Pin It Button from Pinterest is one of my favorites that isn't for work. I love being able to pin anything from it's source directly to Pinterest. I mostly us it to promote my blog (shhh)
D-Mail FINALLY a way to un-send my emails. Dmail ensures only the intended recipient will be able to read the body of your email. As the sender, you can revoke access to any message sent with Dmail at any time, even after it’s been read.
Shareaholic for Facebook much like the Pin It button this one allows me to share content directly to Facebook from any site. Extremely useful when I find an article I like.
Sidekick by hubspot not only tells me when my emails are being read, but also if someone clicks one of the links I send them. It also allows me to integrate my gmails into SalesForce.
SimilarWeb links me to other websites/apps that share common factors with whatever I'm looking at. It's amazing for finding prospects or when I'm boycotting a certain site but still need a similar service
Lazarus recovers form entries for me when my browser crashes or if I do something idiotic and delete everything or go back a page.
The Great Suspender
At work I tend to have... well let's not talk about how many tabs I have open at a time. This extension automatically suspends the tabs I'm not using so they don't use up CPU.
Invisible Hand let's me know when an item I'm looking at would be cheaper somewhere else. It's like... the worlds best shopping assistant.