Dunn is having his best season with the bat, hitting .285 with 31 home runs and 86 RBIs entering Tuesday's action. He also reached two milestones this season, collecting his 1,000th career hit and the 300th home run of his career.
Zimmerman was the Nationals' All-Star representative and hasn't slacked off since playing in the Midsummer Classic in St. Louis. Zimmerman is hitting .305 with 24 home runs and 78 RBIs.
Willingham is arguably the unsung hero of the group. He started the season as the team's fifth outfielder, but has made up for lost time after being inserted into the lineup on an everyday basis in May. Willingham is third on the team in home runs with 19 and has driven in 50 runs.
The Hank Aaron Award, presented by Sharp, is awarded annually to the best overall offensive performer in each league, with each club having three nominees. This is the seventh consecutive year that fans have had a voice in selecting the award winners.
Fans can vote through Sept. 15 to determine the club nominee, and then voting will be held Sept. 16-30 to select the winner in each league. The winners will be announced during the World Series.
Last year's winners were Red Sox first baseman Kevin Youkilis and Cubs third baseman Aramis Ramirez. Originally introduced in 1999 to honor the 25th anniversary of Hank Aaron breaking Babe Ruth's all-time home run record, the Hank Aaron Award was the first major award to be introduced in 30 years.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.