LESS is a wonderful alternative to SASS. <a href="http://lesscss.org/" rel="nofollow">http://lesscss.org/</a><p>nanoc is a very nice Ruby static site generator with a good community and a very active project maintainer: <a href="http://nanoc.stoneship.org/" rel="nofollow">http://nanoc.stoneship.org/</a>
I just proposed the same idea at work. Except I use Django + Compass. The advantage of this kind of prototyping is that you end up with a fully functional and clickable website. And it is much easier to do usability tests with functional websites than with mere static images.