In no particular order ...
1. Chambers 20th Century Dictionary - A gift from my Grandfather when I was a boy, and as much for the inspirational inscription he added inside in his immaculate copperplate hand-writing, as for the joy it has provided over the years since.
2. Way Station by Clifford D. Simak - introduced me to reading Sci-Fi rather than Sci-fi comics, and the simplistic writing style and subtle plots running through the story truly caught my imagination.
3.Henry V by Shakespeare - well, the complete works to be honest, but Henry V is probably my favourite. Was forced to read 12th Night, A Midsummer Night's Dream and the Tempest at school, along with the sonnets, but wasn't really ready for it. Also, de-constructing the characters and motives or theme etc. of each play or verse, also took the enjoyment away from it, for me. Got into Shakespeare again in my twenties and still read, marvel and enjoy the rhythm and writing style to this day - but personally, always best without guidance notes and then just allow myself to flow with the plots and blank verse. Love Henry V for the historical aspects, plot and characterisations that grow and evolve with the story as the play unfolds whilst reading.
4. Foundation by Asimov - for the sheer genius, scale and mastery that draws me in to Hari Seldon's vision, mathematics and psychohistory. Was going to cheat and say the Trilogy, but staying with Foundation, even though the story opens up spectacularly in the later books.
5. The next book I read - hopefully - and then the one after that, and ad infinitum