My favorite "re-read" books are extremely challenging. I.e., those that can't be fully understood on the first reading (or sometimes, the second or third).
- The Fifth Head of Cerberus, by Gene Wolfe
- The New Sun series, by Gene Wolfe
- Riddley Walker, by Russell Hoban
- Edgar Allan Poe, H.P. Lovecraft (probably more due to the arcane language)
Others are just so darn entertaining that I read them every few years, just like I re-watch my fave movies on DVD.
- Startide Rising, by David Brin
- Neuromancer, by William Gibson
- Jorge Luis Borges
- Philip K. Dick
- Watchmen and The Dark Knight Returns graphic novels