Automator World
One of the 200 new features in Tiger is Automator, which is basically a nice GUI app that allows you to automate (or script) various common tasks. Before Automator you would have to learn Applescript, or Perl, or some other scripting language to accomplish much the same thing.
While this is cool, in and of itself, it is even cooler because you can save your scripts (or 'workflows' in Tiger speak) and trade them with your friends. Automator World is the first website (outside of Apple) which facilitates this sharing. Head on over and check it out.