Vintage Season by Henry Kuttner and CL Moore is about tourists in time. It was made into a film, Timescape, starring Jeff Daniels.
There's also the short story, 'Let's Go To Golgotha', by Garry Kilworth, in which tourists go back in time to witness the Crucifixion.
July 4th, 2012, 07:50 AM
Another possibility is Robert Silverberg's Up the Line (http://en.wikipedia.org/wiki/Up_the_Line).
There is also Ray Bradbury's short story A Sound of Thunder (http://en.wikipedia.org/wiki/A_Sound_of_Thunder).