HTML Tidy is a good one for analysing and fixing errors:

http://tidy.sourceforge.net/

If you just want a list you can use the W3C's HTML validator but that can get a little painful if you have loads of pages to check so I'd go with Tidy

I would endorse Rob's recommendation.

I use a free HTML editor, HTML Kit (http://www.chami.com/html-kit/), which has Tidy built in for error checking.

If you use Firefox, there's an extension for it that adds Tidy html checking when you View Page Source from the right-click menu of a page.

The extension can be found at
https://addons.mozilla.org/extensions/moreinfo.php?id=249

Yeah, there's a good firefox extension called Web Developer. It will do Compliance checks etc. too.

I did download the Firefox extension successfully, but when I run it after viewing the Page Source, it catches "errors" and "warnings" in my code. It cannot fix "warnings"automatically as it normally would unless "errors" are first fixed. Of course, the instructions are incomplete (is it just me but techies cannot write instructions for anything?) and it does not tell me how to fix the "errors" first so that "warnings" can be corrected.

Went to the Chami site and after unzipping the program, I'm left with this dll icon that just sits there.

Dazed and confused.

having recommended tidy I would caveat that the best way to fix your code is to sit down with a copy of the spec for html / xhtml and work your way through your source code... there are loads of tools to point out where you went wrong but fixing it normally just takes graft ;-)

Good luck!

Tidy finds errors but does not actually do anything about them. Not helpful at all.