Just to name a few:
http://www.ipad88.com/
http://modmyi.com/forums/
http://www.everythingicafe.com/forum/ipad/
http://forum.tipb.com/ipad-forum/192...er-ibooks.html
P.S. Drill down into any of these sites (and there are many more) and you'll find post after post (ad inifintum) with pitches like I've described.