Manually sorted by browsing most starred JS projects on GitHub (client-side only, all the Node crowd uses 2 spaces).
- Backbone
- Underscore
- D3
- Ember.js
- Angular.js
- Jasmine
- Zepto
- WysiHTML5
- Mustache.js
- keymaster.js
- JSON3
- Prototype
- Scriptaculous
- OpenLayers 3
- Polymaps
- Bootstrap
- HTML5 Boilerplate
- Impress.js
- Modernizr
- Brackets
- LESS.js
- Raphael
- moment.js
- Knockout
- RequireJS
- Mousetrap
- JSON2
- HeadJS
- OpenLayers 2
- Modest Maps
- jQuery
- jQuery Mobile
- Three.js
- jQuery UI
- reveal.js
- History.js
- Respond.js
- Deck.js
- Sizzle
- paper.js
- Leaflet
2 space guys are just using vim for dev I guess. It feels so natural there.