Seek and ye shall find! Sorry, could not resist.
Free, DRM Free, and Beyond the Book enabled, well, there are only a few that I know of from the top of my head (I think all of them have BTB in them, I know Alice certainly does, cannot recall which one, hence two listings)
http://store.kobobooks.com/en-CA/ebo...-wonderland-19
http://store.kobobooks.com/en-CA/ebo...-wonderland-20
http://store.kobobooks.com/en-CA/ebook/dracula-39
http://store.kobobooks.com/en-CA/ebo...d-prejudice-28
http://store.kobobooks.com/en-CA/ebook/frankenstein-25
http://store.kobobooks.com/en-CA/ebo...-fairy-tales-2
Those above are free, so try them, won't cost you nothin'
As for paid books, I know Dan Brown's Inferno has BTB in it:
http://store.kobobooks.com/en-CA/ebook/inferno-20
An edition of Harry Potter And The Half Blood Prince also has BTB enabled too. Sorry, don't have the link to it to hand.
As Peter states, one edition of Lord Of The Rings has BTB, and also one edition of The Hobbit also does too. Again I don't have the links to hand.
There are a fair number of other books with the functionality, but I don't have a complete list to hand.