W3Schools is free, and even has a free certification program:
W3Schools Online Web Tutorials (http://www.w3schools.com/)
Also free is NVU, which is available for all platforms and is a great way to get your feet wet with HTML design:
(Komposer is a newer bug fix version, I haven't tried it so can't testify to its quality compared to NVU - NVU was formerly Netscape Composer, hence the name).
For learning CSS, you might try TopStyle Lite (also free):
TopStyle for Windows - HTML, xHTML, CSS editing in a single program (http://www.newsgator.com/Individuals/TopStyle/Default.aspx)
I usually use w3 schools if I need to look up a tag for something, and they have good tutorials for things like CSS.
I've also found that if you punch "HTML Cheat Sheet" into google, you get a few good lists of tags and what they do.