Compared to you guys I feel boring and old :P I use The Oxford Library of English Poetry vol. II. The poetry has always appealed to me. I've never tried using fantasy but I imagine you can get some pretty unique results.
I'm lucky to have started collecting books when I was a kid so my collection is big (but not big enough), so I usually pick one of my books at random. Close my eyes and pluck type deal. Usually when I have a question I turn to the scrying waters or to bibliomancy (if I don't turn to the spirits for aid). My collection is assorted by alphabetical genre, so when it comes to bibliomancy I tend to go to the section most relevant to my question.
Ive turned to the Dark History of Kings and Queens of England for multiplw questions, enough times I think it's my go to book for broad questions. I also turn to my bible and my copy of Romeo and Juliet. Besides those three books, it's pretty much a random pick.
All Holy books except for anything Islamic
The old and new testaments
The Iliad and Odyssey
Beowulf and The Devine Comedy
I also see tons of influence on the Tarot trumps taken from there
Which is not spoken about often, that will be in my book.