None at all. Id recommend reading other people's code and thinking about it for a while.
Just out of curiosity: if you (or anyone else!) had to make a "must read code" list, what would be on it?
Anything written by Peter Norvig or D Richard Hipp.
Gcc,gnome,openoffice - how not to do something.
FreeBSD,llvm,trac,vim - how to use sound engineering.
Reading code is a great exercise and I've nursed a half-baked post on the topic for years now. However, I'm not sure that code reading is all that's needed.
What is considered good code to read?
If I knew the answer (of at least thought I did) then I could probably finish that post. ;-)
Code Complete 2
Seven Languages in Seven Weeks
The Art of Unix Programming
Before I interviewed at Google, I read the book "Effective Java" Never before have I read something and had an epiphany that not only is someone else is way, way smarter than me, but the advice incredibly powerful and useable. I regularly consult that book, even for non Java stuff.