I recently found my dad's Goodreads.com profile. I'm sure I asked him to join, and I'm not sure how much effort he put into writing his profile but he listed his favorite books:
Gödel, Escher, Bach by Douglas Hofstadter (1979)
The Moon is a Harsh Mistress by Robert A. Heinlein (1966) (review here)
Snow Crash by Neal Stephenson (1992) (review here)
Gravity's Rainbow by Thomas Pynchon (1973) (review here)
The Shining Mountain by Peter Boardman (1985)
I've read The Moon is a Harsh Mistress, but it was many years ago. I do remember loving it. I've tried and failed to read Gravity's Rainbow, but I will try again. I'm afraid of whether or not I got rid of Gödel, Escher, Bach and The Shining Mountain even though I got rid of very very few books, but I will look for them. Maybe starting out with this smaller list will help since it's been two years now and I've made no progress in reading his books.