I've decided to compile a list of some of the best Google+ Chrome extensions. So here they are in order of most usefulness:
1. Start G+:
This is by far the best extension available for Google+. It allows you to seamlessly integrate your Facebook and twitter feeds into G+. Along with that, you can post comments to Facebook and "Like" things on Facebook right from G+. It also supports sharing anything you post on G+ to both Facebook and twitter with the click of a button. Here's the link to go check it out: https://chrome.google.com/webstore/detail/hbgcgahdbgbdenffckohanhobdcnkoip?hl=en-US
2. Replies and more for Google+:
A very useful extension that adds a "Reply to Author" button under every post and a "Reply" button on every comment. This way you no longer have to type out people's names in order to tag them in a post or comment. It also supports hot keys for G+ such as pressing "M" to mute posts. It also causes the Google bar to remain visible at the top of the page no matter how far you scroll down. It can also show Notifications in the tab button at the top of the screen. It has many other useful features as well. Here's the link: https://chrome.google.com/webstore/detail/fgmhgfecnmeljhchgcjlfldjiepcfpea?hl=en-US
3. + Photo Zoom:
A very simple extension that zooms in on pictures when you hover over them with the mouse. It can be configured in the settings to zoom immediately or wait before zooming. Here's the link: https://chrome.google.com/webstore/detail/njoglkofocgopmdfjnbifnicbickbola?hl=en-US
Well there you have it. The top three extensions for Google+. All of them useful in their own way.