My current 5 favorite (client) libraries are:

• React - Angular is fun and easy, until it isn't. And dumping everything to the DOM with jQuery's .append() or .html() was never fun.
• Ramda - Or some other utility library, like Underscore, Lo-Dash. In my opinion, Ramda has better parameter ordering, and automatic currying!
• Reqwest - One of the great benefits of jQuery was getting clean, cross-browser AJAX requests. We can use a smaller library for this. See also, Fermata, Superagent.
• Director - Router library for both browsers and Node.js.
  
• Browserify - Use modules from npm in your client code using require(), just like you would in Node.js! All of the above libraries can be loaded with Browserify.

I tend to prefer libraries that do one job, and do it well. Small, composable libraries help keep your application clean and modular.