I use PSPad (get it from
http://www.pspad.com/).
Its basically a code editor... it has syntax highlighting for more languages than you can possibly eat (CSS, HTML and xHTML... then theres C++, python, fortran, even ini and unix shell; about 20 in all), plus loaaads of tools (html cleanup, css cleanup, error checker, eyedropper, file difference-checker, whole-directory find and replace etc), and tabbed viewing.
Even better than
Kate!
Edit: I also have the Web Developer toolbar for firefox which is pretty damn handy, and use dreamweaver at school... as long as you aren't using SSI or PHP or anything like that its pretty cool.