Well, the OP specifically asked for texts on the fundamental subjects of CS as they relate to web development.

Since you bring up a good point though, what would be useful open source projects to contribute to if you're specifically interested in exploring deeper issues?

For myself, I remember learning about networking (and especially coding the network layer in C) and also a bit about crypto by tinkering with World of Warcraft unofficial open source servers two years ago. Wish I had the chance to contribute something back before real life took over again.