Here are a few I like:
A neat plugin that replaces your form's checkboxes with an iOS style on/off switch.
A new solution to an old problem. This plugin replaces text areas with an HTML WYSI editor. Having used a number of different solutions for editors, this is a much awaited solution.
Tablecloth stays true to its name, prettifying your tables. As their website says: "Making HTML tables suck (a little bit) less."
Automatically generates a Table of Contents for your page based on your headers. This even includes a Scrollspy feature. (Setting one of these up in vanilla bootstrap takes some figuring out, so having it do this for you is awesome!)
Create a "Tour" for your website, highlighting your favorite points and explaining your key features.