Ingy döt Net, creator of Kwiki and Socialtext dude, has created Jemplate -- the first template toolkit for Ajax.
Jemplate is a templating system for Javascript, but it's not just any templating system. It is a complete port of Perl's ubiquitous Template Toolkit. If you don't use Perl, don't stop reading. Perl (and the Template Toolkit) is only needed to compile the templates. The templating lingo itself is Perl agnostic and full featured. It resembles Python, Ruby or Javascript more than Perl.
A lot of you stopped reading, but it's a pretty great open source contribution. Meet Ingy at MuchoCamp.