Some very good sites to learn online courses:

1. https://www.coursera.org/
2. https://www.edx.org/
3. http://nptel.ac.in/
4. 
   

Good sites to learn coding:

1. http://www.codechef.com/
2. https://www.hackerrank.com/

Good sites to prepare for interview questions/ problem solving/ coding tests:

1. http://www.geeksforgeeks.org/
2. http://www.careercup.com/
3. http://www.indiabix.com/
4. Special mention of a book "Data Structures & Algorithms" by Narasimha Karumanchi