A little more information about your tastes would be helpful. I haven't read Ludlum, so I really don't know what he writes.
Larry Turtledove writes some 'decent' (sometimes...it tends to get very repetitive though and its not the best written) alternate history with a very heavy war focus. They tend to be long, ongoing series's. His two major ones are the World at War series (sentient lizards invade at the height of WW2 with technology comparable to ours of the modern day, though a bit more advanced. WW2 tech v. modern tech with alien cultures mixed in). And 'Timeline 151' I think is the name of the other one...basically an alternate history where the South wins the Civil War and goes through the major periods of history (WW1/2/depression/etc) with the south as an indepedent nation and generally playing the role of Germany to the North's 'allies'.
If you don't want to jump headlong into that, his most notable book 'Guns of the South' involves a bunch of South African bigots who get a time machine and go back to give Robert E Lee a few hundred thousand AK-47's, radios, and instant coffee.
Otherwise, Without Remorse was always my favorite Clancy back when I read his shit. (aka, before he became a blubbering, overtly political mouthpiece for the right)
Ender's game is a great, short sci-fi read. Not terribly big on the action, but worth reading.
Got a few others, but a better idea of your favored genres/tastes would help.