Wirify is a bookmarklet that lets you turn any web page into a wireframe in one click. Similar to the Web Without Words, it converts all of the elements on a web page to gray boxes, so you can visualize the page as a schematic without content.
This reminds me of a a technique used in painting and design where one steps back a distance from the canvas or screen and blurs the eyes to get a view of the placement of parts of the design, the relationship of the parts to each other, the white space, and the hierarchy of elements. For people working primarily in HTML wireframes, and for those that have moved from wireframes to prototypes or working code, this would be a great tool for doing the same sort of visual check.
To install the Wirify bookmarklet visit the article at Volkside.