While it's not fool proof. Often when I'm looking for a new author based on liking another author I go to Fantastic Fiction and look at the 'Visitors to this page also looked at these authors' section of the author's page.
On Dan Brown's page the list would be...
James Patterson
David Baldacci
Clive Cussler
Michael Connelly
Steve Berry
Lee Child
James Rollins
Matthew Reilly
Vince Flynn
Tom Clancy
John Grisham
Harlan Coben
Robert Ludlum
Patricia Cornwell
Brad Thor
http://www.fantasticfiction.co.uk/b/dan-brown/