There are lots of lists on various blogs of people’s favorite OS X software (some listed below).
One of my favorite little programs for OS X is SnapNDrag, which is a superior screen capture utility. While OS X comes out of the box with easy screen capture to pdf, that doesn’t do you any good when you’re trying to embed an image into a web page. SnapNDrag supports capture to PNG, JPEG, TIFF, and GIF, which makes like easy. Check it out.
Some lists of essential OS X software:
http://ducttaped.org/2007/4/26/software
http://pbgalvin.wordpress.com/the-best-mac-os-resources/
http://blog.founddrama.net/2007/03/essential-os-x-software-2/
http://andypiper.wordpress.com/2007/03/20/settling-in-with-os-x/
http://fuzzz.gaulin.ca/2007/02/03/so-you-bought-a-new-mac/
http://blogable.net/archives/2007/01/27/10-free-apps-every-mac-user-should-have/
http://www.43folders.com/2007/04/27/my-menubar/ (thanks, Bob!)
Oren Sreebny 