My favorite textbook on algorithms is Sanjoy Dasgupta, Christos Papadimitriou, Umesh Vazirani. Algorithms. McGraw-Hill. 2006. I like it so much that I translated it into Russian. The translation was edited by Alexander Shen and published in 2014 by the Moscow Center for Continuous Mathematical Education.
Online courses on algorithms
I've also recorded a few online courses on algorithms and data structures. The courses consist of lectures video recordings together with tests, programming assignments, and peer-reviewed theoretical assignments: