i've just downloaded both the ibook facsimile of the shakespeare first folio and the shakespeare's sonnets app, both of which, in their different ways, are great things.
the first folio was published in 1623 by john heminges and henry condell. 18 of the plays had been published before in quarto but this is the main source for the texts of pretty much every play we know was written by shakespeare. the ibook is exactly what it says on the tin, a photographic digital version of the first folio. you can flick through and you can zoom. that's it. but if this is your bag, and it is very much my bag, then it's oddly thrilling. it seems expensive at £14.99 but the norton facsimile on paper is £142.50 which makes this version a bit of bargain.
http://en.wikipedia.org/wiki/First_Folio
http://www.ebooktreasures.org/the-first-folio/
the sonnest app contains (deep breath)... the notes from the arden edition of the sonnets, a commentary by don paterson, a facsimile of the 1609 quarto edition and video readings by fiona shaw, cominic west, kate fleetwood, david tennant... all synchronised to the texts, marginal notes, a series of little video essays by experts (as opposed to semi-informed celebrities) and doubtless some other stuff i haven't found yet.
it's like the wasteland app (also by touch press) but better.
don't be put off by the sight of stephen fry on the touch press page. obviously, stephen fry is perfect in certain contexts and he does indeed read a sonnet here but his picture belies the seriousness of the project.
http://www.touchpress.com/titles/shakespeares-sonnets/
this, i think is the future of the ebook. not sinking it's digital teeth into the neck of the physical book industry but doing what can't be done on paper: video, audio, interaction, hyperlinking, synchronising all these things...