When I used to read a lot of code for its one sake, maybe the majority was in books and papers (like SICP, Norvig, Knuth, Kernighan & Whoever, "Functional Pearls", ...) which explained points the author thought especially important. There's lots more great code to read without the extra commentary (especially nowadays) but you do have to work harder to find the lessons.

To me it was especially valuable to always be asking "how might I write this better (in some sense)?" whether it's great code or not. When it's especially good you'll still think of plausible improvements, and maybe the lesson is in figuring out how they're not actually such an improvement as you think.