Those book I sit down with on a Sunday morning (or any morning I am free the whole day) and read from start to finish in one sitting, always greedy for more.
The Hitchhiker’s Guide to the Galaxy by Douglas Adams
Any Foundation Series by Asimov
Storm Front (and few of the other before they got happily larger in size) by Jim Butcher
The Invisible Library by Genevieve Cogman
Legend by David Gemmell
Any Nightside Novel by Simon R. Green
Any Secret Histories Novel by Simon R. Green
Hounded by Kevin Hearne
Any Discworld by Terry Pratchett
The Silent Regard of Slow Things by Patrick Rothfuss
Mist Born series by Brandon Sanderson
and probably a few more once I think on it, updates to come.