I have created a new section on this blog called Apps to Check Out. You'll find it on the right-hand sidebar. Please keep in mind that these are not links to the actual apps. Something good to know is that many of them are offered in a Lite version which is free. What's nice about that is you can use them for awhile to determine if they're worthwhile.
Some book apps worth chasing down are the iPad books found at Oceanhouse Media (through the iTunes store) and Nook Kids found through Barnes & Noble. Please let me know if you bump into quality titles elsewhere as I would love to start a bookshelf on our classroom iPads. We have yet to invest in this area and the only iPad titles I can share (other than stories found on TumbleBooks) are those I have purchased for my personal iPad 1.
I will continue to add to this list. For the record: the order of the listing is random.