Quplo may be the most promising HTML prototyping tools I've seen for UX designers who know a little HTML and would like to do HTML prototyping, but either don't have the chops to build the interaction by hand, or are lazy like me.
The web-based tool allows you to build multiple prototypes using a combination of standard HTML/CSS. If you can do JS, the standard JS libraries are available to include in your pages (or sheets in Quplo lingo).
Quplo provides some really simple syntax and markup language, called "flow," for creating variables, loops, conditionals, layouts (like master templates), parts (reusable pieces of code like UI components, menus, etc.), and including browser, get and post vars.
You can even specify a "redesign" prototype and provide a URL, and it'll ingest the HTML for that page as a starting point for your prototype. Cobble together a bunch of pages and you have an interactive HTML prototype to demonstrate your pages and state changes. If you need to, you can download a compressed .zip of the XML files in your project.
This is easily the best thing I've seen for HTML prototyping for non-programmers that I've seen. It's like what my Protokit wanted to grow up to be. :) Sick stuff for the UX k1Ddi35. You can bet I'm going to campaign for a way to get Mockups into this tool.