Putting print magazines on (not released at the time) tablets was a hot topic last winter. We saw Wired's Tablet Edition demoed, but that was written in Adobe Air and so is being re-engineered to run on the iPad, thanks to the Apple/Adobe kerfluffle. ETA unknown, as far as I can tell.
We also saw a version of Sports Illustrated for tablets back in December, but that was just a mock-up, complete with a fake hand manipulating the screen. It wasn't nearly as impressive at the time, but yesterday at Google's I/O a prototype was demoed. This version was written in HTML5 and running on a computer, not a tablet (though we're assured it would work on a tablet, too). Rather than go the app route, Sports Illustrated is building its 'tablet edition' on the web; you'll access it via browser, on any hardware that has an HTML5 compliant browser. No Flash or other plugins required. Of course there are still questions, and this is still a prototype. The biggest question I have is what loading times are going to be like. Clearly this demo is being run against local content; what the 'real world' online experience will be like is still very much open to question. Caveats aside, it's a pretty impressive demo when you keep in mind it isn't using any kind of plugin. Here's the video from yesterday. I'm embedding it in this post but you should really watch it in HD if you can.
And for comparison's sake, here's the rendered version they were showing last December.