They'v released the complete list of titles ( here), and it looks like at least some are current in-print books. They're spread across several genres, including Cooking, Kids, Classics, Humor, Lifestyle, Fiction, Sports, History, True Crime and Reference. Some of the free titles include: The Good Housekeeping Cookbook, Cristina Ferrare's Big Bowl of Love, Creating Your Best Life, Glory in the Fall: The Greatest Moments in World Series History, 21st Century Crossword Puzzle Dictionary, My Boyfriend Wrote a Book About Me and timeless favorites including Secret Garden and Robinson Crusoe.
Update: Mike Cane pointed out that I missed an important detail. This isn't a trade in program. You just have to show the old ebook reader when you buy the new one. That just made the deal a lot better. Now you can get the free ebooks with a new Nook without giving up your still working older ebook reader.
B&N could really sell a lot of Nooks with this.