I recently came across a well designed add-on to upload files with Angular called angular-file-upload. It's highly customizable, takes full advantage of the HTML 5 file drag and drop, progress, and size API, and was easy to use.
I wrote a basic example of it and put it up on JSFiddle to share. You can choose and drag and drop multiple files onto it, then upload each separately. Take a look at its API for more in depth options and use cases.