C/C++

Learn C

This is a great place to start learning C without worrying about compilers or settings up a dev environment at first, just get your feet wet.

The C Book

The C Book; amazing online free book for learning the C language. It’s a little harder to digest than some newer tutorials, but it’s well-written and covers what you need to know; this is what I used when learning to program initially.

CPlusPlus

Certainly not the most stylish website, but an excellent C++ reference site with forum and tutorial sections as well, I’ve been using it for years.

The New C Standard

A tad dry perhaps, but really rather comprehensive; probably better as a reference or deeper look into the language, not likely the best place to initially learn from.

Matters Computational

A rather interesting look at quite a few different algorithms and computational problems with ideas and example code solutions.

C++ Annotations (actual content)

Somewhat dry, and not entirely Windows-friendly as it has a decently-sized section on forking processes (which isn’t really usually supported by non-unix systems), but good content that seems to be kept up-to-date.

Network Programming

Network programming, especially in a lower-level language can be a real pain, and quite frankly… frustrating. This can help ease some of the cognitive burden and trial and error for doing that in C/C++.

You should also be aware of the The Definitive C Book Guide and List, however, just keep in mind that resources listed there are usually books that require purchase.