Print Wirelessly from your iOS4.2 device with AirPrint Activator

The AirPrint Activator  enables an  iPad or iPhone running iOS4.2 to wirelessly print to any shared printer connected to a Mac or PC.

(Apple officially only allows you to print to an AirPrint-enabled printer from HP.)

Update Jan 14, 2011: Removed link to Windows version as it was 404 and updated link to new, renamed version.