Here is a great HTML tool. I wasn't able to find any reference to it in the forum so I think this is the first post describing it. The tool is called The HTML Reference Library. It's a help application that is the most useful HTML reference I've yet seen. It's very easy to find the information you're looking for and it even indicates which browsers are most likely to support the newer features.
The downside is that the tool requires that you use Microsoft Internet Explorer version 4.01 or greater and that you have installed the HtmlHelp 1.1 ActiveX controls (downloadable from Microsoft). Still this is such a wonderful reference, you'll wonder how you got along without it, unless of course you never need to code any HTML.