Adobe has sponsored the May 2011 issue of Wired magazine for the iPad, so you can download the May issue free through mid-May. As an early adopter of the Adobe Digital Publishing Suite, Wired keeps pushing the boundaries of what can be done with this new software suite.
Just download the Wired app, and then launch it on your iPad. You will see a list of all the issues available to purchase, and you will see the May issue listed as free.
See the Adobe Digital Publishing blog for more info.