WordPress - because it's extremely crappy but at the same time insanely accessible. Lots of lessons to learn. Passenger - code looks good even though it's C++

WordPress - because it's extremely crappy but at the same time insanely accessible. Lots of lessons to learn. Passenger - code looks good even though it's C++ Rails 3. Beautifully structured application foundation that's not just a pretty piece of code, it's tested and works. JScheme. Reading this clean implementation and re-implementing it yourself gives a good basis of understanding for lisp.