Ruby has a wide variety of HTML/XML templating engines, but none of the ones I’ve found work the way I’d like. It’s quite possible I’ve overlooked some, though.
My current gold standard for templaters is the Python library Genshi (which was inspired by Kid)—what I like about these is that your templates are valid XML: the parameters and control structures are expressed as special XML attributes and tags. This makes it easy to edit your templates in syntax-checking XML editors, and guarantees that your app serves valid XML or HTML.
But as I said, none of the Ruby template engines I’ve seen work this way. They’re all either generic macro systems that intermix markup and Ruby (like ERB), or they’re ruby APIs that output markup (like Builder, HAML and Markaby). I don’t really like either approach.
If you’ve got a good suggestion, I’ve got a gold star ready to stick on your forehead!