Clive Cussler has a large series starring his character Dirk Pitt--pretty much straight action-adventure type stuff.
James Patterson's Alex Cross series is pretty popular.
If you like historical fiction, Wilbur Smith is one of the best--he has a few different series: The Egyptian, set in ancient Egypt, is probably my favorite.
Stephen King does the Dark Tower series, which is pretty popular, but I've never been able to get into it.
And of course, Tom Clancy has some great books starring Jack Ryan.
I tend to read more fantasy, so I'm not sure if you would be interested in those:
Wheel of Time - Robert Jordan
Sword of Truth - Terry Goodkind
Thomas Covenant - Stephen R. Donaldson
A Song of Ice and Fire - George R.R. Martin
The Malazan Book of the Fallen - Steven Erikson
Memory, Sorrow, and Thorn - Tad Williams
The Dresden Files - Jim Butcher
Riftwar Saga - Raymond E. Feist
and Lord of the Rings - JRR Tolkien