Witch
Witch is a very cool Mac OS X utility to switch not only between applications, but also between their windows. You’ve got to see it to appreciate its slickness :-)
This is a single archived entry from Stefan Tilkov’s blog. For more up-to-date content, check out my author page at INNOQ, which has more information about me and also contains a list of published talks, podcasts, and articles. Or you can check out the full archive.