Tough i have so many.(over 2000 books and counting)
Most read would be.
Stranger in a strange land.Heinlein
the lensman series.E.E.Doc.smith
Fountains of paradise A.C.Clark
the number of the beast.Heinlein
Starship troopers (refuse to watch the film - producer should be shot).
The songmaster. Orson scott card
Foundation series. Azimov
The moon is a harsh mistress. Heinlein (bit of a pattern emerging)
The nights dawn series. peter f hamilton.
Just finished the dreaming void by same author.brilliant read going to have to wait a year for the next installment.