4
TopStyle lite is bundled with Studio MX. I believe the Pro version is what is integrated into Dreamweaver. TopStyle Lite is nice for a free editor, but it does not include the validation tools needed to verify that the CSS will work with IE, NN, and MAC.
TSW Webcoder is another fine editor, but I think it only validates HTML.
There's always the option of bookmarking the
W3C CSS Validator. The downside is that you won't be able to capitalize on each browsers capabilities, but the advantage is that your site would look the same to all visitors.