This thread is a good idea, but it's not ideal. It's hard to read through to find the code you want, and to check that you have the latest word on the best solution to any particular problem.
So I've created a "HowTo" page in the wiki to hold the CSS hints and tips.
But I haven't filled in very much yet. Contributions (perhaps culled from this very list!) are very welcome. I'll work on it some more as I have time.
You can also read this page from the main page through the "HowTo" link under FAQs.