I use the chart on page 70 of my Weber’s Real Grilling (2005) cookbook:

rare 120-125˚ F (USDA recommends not cooking meat this rare)
medium-rare 125-135˚ F (USDA recommends 145˚ F)
medium 135-145˚ (USDA recommends 160˚ F)
medium-well 145-155˚ F
well-done 155˚ F + (USDA recommends 170˚ F)

The lower values are “chef standards”. The USDA does not agree, so use these lower values at your own risk. The chef standards listed above agree with several of my other grilling cookbooks.