Whatever the reasons are, if you feel like you're lacking in some portions of your education. Or even if you just need extra resources to further pursue what you are learning in class, maybe even to go further with what you have learnt. It is always good to have some reliable resources for online course material to look into for supplemental learning.
Over my years at university I have stumbled upon quite a few good online learning resources. I am not able to remember them all but the following are some good places to start:
Basically an aggregation for many other universities online lectures.
OpenCourseWare (By MIT):
MIT has been having online courses published for quite a while and have been offering online video lectures for everyone since around 2005.
The Khan Academy:
Focus on math/calculus education and is mainly started and maintained by one man. It is a whiteboard style of learning and is a very understandable resource.
Digital Technologies by Xiph
An extremely extensive yet easy to understand explanation of digital technologies.
And of course there are other resources like wikipedia/google/textbooks/youtube but these are just a few of the reliable resources I have discovered.