One of my web heroes Jonathan Snook has released a great digital book (website, ebook and print versions) about writing better CSS called SMACSS. I have read and re-read this thing several times already:
SMACSS (pronounced “smacks”) is more style guide than rigid framework. There is no library within here for you to download or install. SMACSS is a way to examine your design process and as a way to fit those rigid frameworks into a flexible thought process. It is an attempt to document a consistent approach to site development when using CSS.