To reach light roast (also called New England, Half-City, or Cinnamon), roast your beans just past the first crack. That's an internal temperature of 356 to 401 F.
For medium roast coffee (also called City, Regular, or American), continue for a few more minutes until just before the second crack. The internal temperature should be 410 to 428 F.
If you prefer medium-dark roast coffee (also called Viennese, Continental, Fully City, Light French, or Light Espresso), stop roasting during or right after the second crack. You should see oils on the beans and reach an internal temperature of 437 to 446 F.
For dark roast coffee (also called French, Espresso, Turkish, Italian, Dark French, or Heavy), continue roasting for a few minutes after the second crack. You should see plenty of oil on the beans and reach a temperature between 464 and 482 F.