Science fiction can be influential in different ways. Maybe the story is a political allegory that made people think. Maybe it was a cautionary tale of science unrestrained by ethics. Maybe it inspired engineers to develop useful technology. Maybe it stretched the definition of science fiction or opened doors for other writers. That said, any such list will be subjective. I would have included Frankenstein and Fahrenheit 451, but then again, I'm not a sci-fi expert. Read the list of Science Fiction Books That Forever Changed The Genre at Lifehacker. Are your favorites on it? -via the Presurfer
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The only omission I might suggest is "Ender's Game" by Orson Scott Card. It was a well received return to adventure based SciFi that can be appreciated without the need to be aware of social or psychological commentary.