To what temperature should steaks and roasts be cooked?

Because bacteria reside only on the surface of whole-muscle beef, the meat needn't be cooked to an internal temperature of 160°F, as is required for ground beef. Steaks, roasts, and the like may be cooked to an internal temperature of 145°F (medium rare), 160 degrees F (medium), or 170 °F (well done), Use a food thermometer to ensure meat reaches a minimum temperature of 145°F. If processed marinated beef has been injected with solutions of various ingredients to increase juiciness, these ingredients may alter the color at a given temperature, making the beef appear more or less done. The label will tell you whether the meat has been “enhanced.” If it has, be sure to use a food thermometer to decide if the beef is at the degree of “doneness” that you want. Appearances can be deceiving.
 
Source(s):
American Meat Institute Fact Sheet "E coli O157:H7"
Susan Brewer, Ph.D. University of Illinois, Department of Food Science and Human Nutrition