Gosh, this is really a hard question as you can see from the apparent lack of enthusiastic answers. If only you asked where can you find BAD, AWFUL code I can guarantee there would be a lot more links. I mean, there are movements devoted to producing as bad code as possible. Take a look at Obfuscated C Code Contest [ioccc.org]. You can learn from negative examples as well, and they are much easier to find.