Personally, if I am at a safe distance, I would just let Mr. Snake alone and go on about my business. But circumstances vary, and if you must do the critter in, a thrown rock is a pretty good tool (not quite as effective as a shovel). You can channel your inner Nolan Ryan.....

Rattlesnakes are pretty good at keeping down the local mice, and mice have probably killed more people as a carrier for infectious diseases (hantavirus etc) than rattlesnakes.