Nascar.com is the official site of NASCAR and has a page for full results from the previous season to find out who won each race. The site also has a page with schedules for the upcoming season, and race results are added as they happen.
ESPN.com also contains the latest NASCAR results and headlines, with a drop-down menu for selecting the year for a certain result. This function goes as far back as 1949 up to the current year. It also gives the winner and pole winner of each race.
ESPN.com also states that it has live race coverage for NASCAR.