This is what most people think of when they think of "science fiction". The future, technology, robots and invasions of Earth by little green men. But sometimes hard SF cuts so close to where we actually are that you have to look hard to see the twists that take it out of mainstream and into science fiction. One of the earliest practitioners was the French novelist, Jules Verne. His science was so hard and so tight he extrapolated much less than people think, on occasion. For example, his 'Nautilus' is often said to foreshadow "successful submarines" by pedants who do not realise it was named in honor of a working submersible of the Napoleonic period. He also established the formula that the science will be shown to the reader as the source, motivation, obstacle, and solution of an adventure story.

One sub-sub-genre of hard SF you might want to check is Cyberpunk.

• I,Robot and The Gods Themselves by Isaac Asimov
• Heavy Time and Hellburner by C.J. Cherryh
• Downbelow Station, 40,000 in Gehenna, Cyteen, Merchanter's Luck, Rimrunners, Finity's End and Tripoint by C.J. Cherryh
• The Moon is a Harsh Mistress by Robert Heinlein
• Dune, Dune Messiah, or Under Pressure by Frank Herbert
• A Spectre is Haunting Texas and The Wanderer by Fritz Leiber
• Ringworld by Larry Niven
• The Weapon Shops of Isher and The Weapon Makers by Fred Saberhagen
• Frankenstein by Mary Shelley. Even though this one is straight horror, it is also one of the first pure SF books ever written.
• Riding the Torch by Norman Spinrad
  
• The Blue World by Jack Vance
  
• From the Earth to the Moon and 20,000 Leagues Under the Sea by Jules Verne
• The Time Machine, The Island of Doctor Moreau, and Things to Come by H.G. Wells