There are many sites out there: Google for "css-discuss" for example, then there's: alistapart.com, stopdesign.com, veerle.duoh.com, zeldman.com, a lot of sites really...
But the problem is Internet Exploiter. it will ruin perfectly valid CSS designs, because the browser has many CSS bugs. it is bung.
This shows a list of it's known CSS bugs:
CSS is not supposed to be hard, but Internet Exploiter has made it that way, if it wasn't for IE's bugs, there wouldn't be half the hassle with CSS.
Either keep it simple, use simple CSS that avoids IE's bugs in the first place...
...or (but I wouldn't recommend this, unless you are an advanced CSS user), then do what I do, and write am additional "fix" CSS file for IE called ie6fix.css and load it through conditional comments, but once again, I don't recommend this unless you have had some experience with CSS, and fully understand IE's bugs.
My site, http://robvdl.sitharus.com uses an IE fix file to fix IE's bugs/quirks.