Some books featured on the page right now are American Gods, The Pioneer Woman Cooks, Telegraph Avenue, Prague Winter and more! Visit the page to watch a great video that features authors such as Michael Chabon and Colin Powell discussing their enhanced e-Books.
HarperCollins is calling them deluxe ebooks and not enhanced ebooks, and the site currently highlights 13 titles published by HarperCollins.
You cannot tell this from the webpage but that's only fraction of the enhanced ebooks published by HarperCollins; I found some 4 dozen titles in the Kindle Store and there are probably more titles in other ebookstores.
And for those who aren't familiar with enhanced ebooks, HC has also posted this video on the webpage:
HC distributes enhanced ebooks to iBooks, Nook, and the Kindle Store. The ebooks can be downloaded to iPad, iPhones, Nooks, Kindle Fires and more, all at the appropriate sites.