Chromey Calculator is a great built-in calculator, which uses Google and Wolfram|Alpha to generate its results. As a consequence it's surprisingly powerful, and can cope with natural language requests: e.g. "4567 is what % of 7800".
12: Trash Can
Great though tabbed browsing is, if you have lots of tabs open it's often easy to close one inadvertently when pruning those you don't need. Rather than go hunting around in your browser history, Trash Can keeps a record of your closed tabs so you can re-open them if you need. Simple, but essential.
13: Stumble Upon
Though not always the most fashionable of social news services, Stumble Upon is one of the most successful and its Chrome extension/toolbar is excellent. Never was there a better way of wasting time on the internet, finding new and potentially funny, or interesting, pages to enjoy.
14: Send from Gmail
Click on an email link on a web page and it will generally try to open Outlook, or Windows Live Mail, even if you don't use either. Send from Gmail ensures such links open a Gmail compose windows instead.
Mayhap an article uses a word you don't recognise? Then you'll be needing the Google Dictionary extension. By default it will pop-up definitions when you double click on a word, but it can also be set to 'Ctrl + double-click if you prefer'. Clicking the 'more' link takes you to larger page where you can view other potential definitions, examples of the word's use in other online articles and links to other online dictionaries.
And the ones that should be part of Chrome anyway...
There are quite a few examples of such extensions that ought to be part of Chrome as standard, but the two that stand out to us are the Downloads extension and the RSS Subscription Extension. The former adds a shortcut to the Downloads tab to the toolbar, while the latter gives you a Firefox-esque icon in the address bar where you subscribe to a website's RSS feed. Quite why they're optional extensions we're not sure, but we recommend you get them nonetheless.
That concludes our picks of the best Chrome extensions out there. Let us know what extensions you can't live without in the usual fashion.