I just posted a link for Mishoo's website, simply because of the fact that he probably comes up with some of the coolest DHTML driven, cross browser free software out there.
I personally use his HTMLArea WYSIWIG editor, which is great, and is backed by a large developer community.
I recently came back to the site, as Flex-Mx started talking about his great DHTML Calendar. It is a seriously nice piece of work, and will probably replace the DHTML Calendar I've been using in some other places.
I also love his business model for free software – feel free to make a suggestion on the product, however, add a donation to the suggestion, and you get more influence. The more donations given to a particular suggestion, the more likely it is to be added into a product. In some circles that may be called bribery, but in this case I think it's just smart ;o)