(Unfortunately my copy of the movie 2010 hasn't arrived yet or I would post an image from the film of his only film cameo. That image is from the back of The Fountains of Paradise.)The novel is easy: 2001. Written at the same time as he was working with Stanley Kubrick on the movie Clarke's vision of humanity's encounter with aliens far superior to us stands on its own. The wonderful ideas that would have made bad exposition in the film are gently slipped into the novel to make it a richer experience. I know that Clarke fans generally prefer Rama or Fountains of Paradise which I personally didn't care for; perhaps that makes 2001 the Clarke book for people who didn't care for his other books.
The story is "The Nine Billion Names of God" where he merges the mystical and the scientific into one tight, stunning story. The technology is out of date but the concepts are not. It also has one of the greatest final lines in science fiction.
