This year I (finally) made the switch from Firefox to Google Chrome, and I was very impressed by the wide range of extensions that Chrome offers. Here are the top 5 (free) extensions that I feel are essential.
Blank New Tab Page: If you hate the new tab page in Chrome like I do, give this extension a try. When you open up a new tab, it simply shows a blank page, nice and simple.
Block Site: If you suffer from distractions online and need help staying focused, this is the perfect tool to block any unwanted websites. You can control the times you want to block sites and disable the entire extension at any time (although you shouldn't!)
AdBlock: If you hate annoying ads then you need AdBlock. There is also Adblock Plus, an alternative option that works well too. Some sites annoyingly prevent you from visiting them without disabling AdBlock, so you can add them to the whitelist, either for that specific page or the entire domain.
Notifier for Gmail: Quite possibly the most useful chrome extension here. It offers a popup Gmail menu that you can use to check your unread emails, either in summary or full format:
You can connect as many Gmail accounts as you want!
Google Hangouts: A native google hangouts pop up app that shows all of your Google Hangouts activity. You are notified of all new messages that arrive.
I hope you find these extensions useful like I do!