When I was younger I read a ferocious amount, mostly science-fiction and fantasy, but these days I don't seem to have as much time. Still, my list, for what it's worth, in no particular order:
Nineteen Eighty-Four (George Orwell)
In Plain Sight: The Life and Lies of Jimmy Saville (Dan Davies) One of the most chilling and disturbing books I have ever read, not only to read the depth of Saville's crimes but also the culture of personality and the sense of appeasement that allowed him to get away with it for so long. The only book I have ever read where I wished to kill the central character, even though he was dead already.
The Iliad (Homer)
The War of the Worlds (HG Wells)
The Prince (Niccolo Machiavelli)
Somebody's Husband, Somebody's Son (Gordon Burn) The life and crimes of Peter Sutcliffe, the Yorkshire Ripper
The Father of Forensics: How Sir Bernard Spilsbury Invented Modern CSI (Colin Evans)
The True History of The Elephant Man (Michael Howell and Peter Ford)
Charles Dickens: a Life (Clare Tomalin) I think this is the only book where I cried like a baby when he died.
The Hitch-Hiker's Guide to the Galaxy (Douglas Adams)