Robert Ludlum - similar to Clancy, tons of books
damn, can't remember the author's name - the Dirk Pitt (tm) Series. I get a giggle from a registered name - Dirk always saves the day after inumerable feats of superhuman strength and clever ness.

Sci-Fi, etc.
Arthur C. Clarke - Rama Series
Robert Heinlein (sp?)
Jose Farmer
Piers Anthony (for light fun)