- Let's Build a Compiler, by Jack Crenshaw.
- Compiler Construction - Niklaus Wirth (PDF).
- Matt Might teachings about compilers.
- Compilers at Coursera
However, those who wants to be serious about compilers should consider acquiring the books:
- Compilers: Principles, Techniques, and Tools. Either 1st or 2nd Edition. I've got the 1st edition from AbeBooks, the basics are still the same today compared to 30 years ago (tokenizer, parser, syntax driven translation, intermediate code generation).
- Engineering a Compiler, Second Edition. This one is a good book too, and it talks in more detail about Recursive Descent Parsers, which in practice is what many compilers are doing today (ie, gcc for C++). It is a simple technique, and you can write a RDP by hand easily.