- GNU grep (source, maybe start here)
- TTYtter in Perl (source)
- Knuth's literate programming version of adventure
- The Python implementation of deques
- Some Ruby: rspec-expectations and Rubinius
A couple of good lists (thanks to @DanielleSucher)
- http://seanstickle.com/2013/12/27/great-works-of-source-code.html
- http://blog.fogus.me/2013/12/27/the-best-things-and-stuff-of-2013/ ("Favorite code read")
- Code to read when learning Go
and also: