This may seem obvious, but bringing up the force quit window (hit Command-Option-Escape) and double-clicking one of the listed apps will bring it to the front. It may not be elaborate, but it works -- and it stays on screen after switching, so you could leave it open and position it out of the way for easy repeat access.
[robg adds: I'm not sure I'd recommend using the Force Quit dialog as an application switcher, but it clearly works in that role.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2004041916595021