Smart Scroll (formerly Smart Scroll X) offers smooth and easy iPhone-like scrolling:

• Super Scroll makes your scroll wheel or trackpad smoother, faster and more comfortable. And it lets you reverse scrolling on the Mac to match your iPhone. Try it!
• Grab Scroll gives you a Hand tool to easily move (and "throw"!) any window's contents.

Other features include Universal Scroll Keys that let you scroll from the keyboard, FileMaker Pro and AppleWorks enhancements, and more.