How do I provide content to sponsors in a way that makes their jobs easier?

Create a shared Dropbox folder and send an e-blast to all sponsors before each race with the link. Contract with videographers and photographers who upload content in real-time during the event. This allows sponsors to grab relevant photos and videos immediately while the race is still happening or just finished. Don't make sponsors wait 10 days for content - if you pop champagne on the podium, that photo should be available that night. Real-time content delivery lets sponsors post relevant content while people still care about the event.