Pusher

Pusher is a tool that installs world-famous Installer.app that gives access to numerous award-winning tools for the iPhone and allows you to use best of both App Store and Installer without compromising your security.

Pusher will put Installer.app onto your 2.0.2, 2.1, 2.2 or 2.2.1 iPhone (both 2G and 3G) as well as a number of other goodies.