Since we are yet to see the first Angular2 release (almost there, but not yet); most Angular2 third-party resources may not provide the most up to date information, so the best place to learn Angular right now is really the official Angular documentation i.e.
https://angular.io/ , because it is updated quite often.
1. If you are looking for a book to learn in a sequential way then ng-book is a good option. ng-book is updated regularly however it is not free.
https://www.ng-book.com/2/#features
2. New blog posts are also a great way to learn about certain Angular topics. Examples:
2(a): http://blog.thoughtram.io/categories/angular-2/
2(b): http://angularjs.blogspot.com/ (Has both Angular 1.x and 2.x articles, written by Angular core developers)
3. Learning by observing:
3(a): material2 is a library, being developed by the Angular team itself, that is based on Angular2 and is frequently updated to use the latest Angular2 version (currently RC5). I refer to the material2 source code to learn the best way to write my own Angular2 app and custom components: https://github.com/angular/material2/tree/master/src/lib
