Science Fiction
The VALIS Trilogy by Philip K. Dick
Amazon
ASIN: B006C3M1WY
Fantasy
Legacy: Arthurian Saga by Mary Stewart - (Four book bundle of Crystal Cave, The Hollow Hills, The Last Enchantment and The Wicked Day)
Amazon
ASIN: B007QXWCQE
Mystery/Suspense
Girl With the Dragon Tattoo Trilogy Bundle by Stieg Larsson
Amazon
ASIN: B0067AC5KA
There are plenty of Sherlock Holmes collections out there, but this one in particular is very good. Worth the money, I think:
The Complete Sherlock Holmes (Heirloom Collection)
Amazon
ASIN: B007PT1PEY