Among the 70 volumes of Arthur C. Clarke's written work, the following are most essential. This list is, of course, by no means exhaustive.

Childhood's End - 1953
Against the Fall of Night - 1953 (revised as The City and the Stars, 1956)
The Nine Billion Names of God - 1967 (collection)
2001: A Space Odyssey - 1969
The Wind from the Sun - 1972 (collection, revised 1987)
Rendezvous with Rama - 1973 (Hugo, Nebula & John W. Campbell award winner)
The Fountains of Paradise - 1979 (Hugo & Nebula award winner)
The Songs of Distant Earth - 1986
The Hammer of God - 1993

Forthcoming
The Light of Other Days - January 2000 (with Stephen Baxter)