Eric Meyer by far...it's great to have these books on hand, too. I'd strongly urge you forget the ebook because these are much better references even after you've absorbed it!
Get FireFox if you don't already have it, and an add-on called FireBug. As you learn, it will become a more and more amazing tool. You can make changes to a page's CSS on the fly and see their effect ... for me this is the most powerful way to learn.