Among my absolutely essential Google Chrome Extensions are Xmarks Bookmarks Synchronizer and LastPass. There are a few more that I'm still looking for like Key Scrambler that is available for Firefox. I would assume that once all these extensions are available the switch from Firefox to Google Chrome would be more permanent. But right now Google Chrome Browser does lack in terms of add-ons, extensions and plugins when compared to Firefox but like all things Google is getting there.
For now, you can check out a list of must have apps and extensions for Google Chrome Browser.