One of my favorite authors is Steve Berry. His books feature Cotton Malone, a retired US Justice agent who is now a bookseller in Copenhagen that can't escape his ex-boss as he travels the world on missions solving great historical mysteries, like discovering the Library of Alexandria and Alexander the Great's tomb. I also like the Alex Berenson and Vince Flynn novels, which are political spy thrillers.
Are you looking for books with strong female characters or by a female author? You might want to try Gayle Lynds. In addition to her own books, she co-wrote several with Ludlum in his Covert-One series. Most people link Daniel Silva to his Gabriel Allon series (which is very good). However, I also enjoyed his book The Unlikely Spy set in WW2 which features a female Nazi spy. A light and fun spy novel is Olivia Joules and the Overactive Imagination by Helen Fielding (of Bridget Jones fame); I wish she would write a sequel! I also like the Noel Hynd books, which are Christian spy thrillers starring a female US Treasury agent.