Useful and/or interesting web sites
The Art of Unix Programming - Eric S. Raymond's book about Unix development culture.
The Structure and Interpretation of Computer Programs - MIT CS text book.
Standard C - A guide to C.
Articles by Paul Graham - "Hackers and Painters" and more.
An introduction to data structures. - MSDN articles covering common data structures.
Smashing the stack - exploiting buffer overflows.
RFC Index - RFCs make the net go round.