A good way to improve as a developer is to look at well-written code.
What examples of beautiful, well-architected Javascript have you encountered?
Note that I am not looking for a debate about the language itself. It has good parts and bad parts; some like it, and many hate it. Let's leave that discussion to other threads.
Though it's an article rather than just a listing of code, I'd nominate Douglas Crockord's article about Top Down Operator Precedence Parsing in Javascript. It's no surprise given the source, but he makes excellent use of Javascript's capabilities to develop code for a very neat approach to solving a non-trivial problem.
It depends -- personally, I've found Underscore.js' code to be very enlightening for how to structure simple toolkits. They just added an annotated version as well.
Knockout is also quite interesting, and presents a few techniques that you might not see in a more normal library like jQuery or Mootools.
Not that the code for jQuery or Mootools (or Dojo or YUI or ... you get the idea) is bad -- quite the opposite! There is an amazing amount to be learned from these libraries, and I cannot recommend enough looking up the declaration of a method that you find intriguing in any of these libraries and following the breadcrumb trail -- it's a real learning experience!
So dig in ... there's lots to see, and very little time to see it!