https://github.com/ducksboard/gridster.js - http://gridster.net/ Good but not maintained, looks pretty heavy
https://github.com/troolee/gridstack.js - http://troolee.github.io/gridstack.js/ More modern maintained version of gridster but needs lodash + jquery UI
https://github.com/ManifestWebDesign/angular-gridster Angular only
https://github.com/hootsuite/grid - Not flexible enough - no draggable corners
https://github.com/ModelN/sDashboard
https://github.com/McPants/jquery.shapeshift - More Masonry than grid, but supports dragging
http://ksylvest.github.io/jquery-gridly/ - Only 2 sizes, but quite clean
http://packery.metafizzy.co/ - More Masonry than grid, but supports dragging
https://github.com/hootsuite/grid - Fixed size resizing