Where can I find additional look and feel implementations?

The slaf look and feel (http://www.memoire.com/guillaume-desnoix/slaf/index-en.html is one such that look and feel that is itself customizable.

The Up to Speed with Swing book includes a (partial) Chrome look and feel, with the source code for the ButtonUI available online (http://www.manning.com/Gutz2/Source.html).