Well, I just completed a small gadget that for me as a developer is very useful: Clip Collector. 
This gadget essentially keeps track of the last 120 items you copy to the clipboard. You can then cycle back through the collected items to put something back on the clipboard to use later. Additionally, you can manage the clips by deleting the ones you do not want to keep. Again, this is a very simple gadget, but then again that is rule #10.
One important note is that this gadget works with TEXT ONLY. This is because the following function only supports raw text:window.clipboardData.getData()
Other than trying to figure a way to hack some API from the Gadget, I cannot see how I can get any other formats via DHTML/JavaScript. If anyone has some tips and can point me to a link, I will update the gadget for sure.
As for gadget creation in general, I am finding myself falling back to a couple of places when building gadgets, so here are the links I ise the most:
Additionally, I run a lot of searches on Live.com for implementation examples in JavaScript – not specifically related to Gadgets. There are lots of interesting things you can do with JavaScript and just when you think you have grasped the language, there is something else to learn.
Anyway, I am interested in your feedback on the latest gadget: Clip Collector. Let me have it! 