A quick search of some national motorsports events (full scale) in 2012:
August 5-7 Unlimited Hydroplane Boat Races in Seattle, Washington
August 17-19 2012 National Truck & Tractor Pulling Championships in Bowling Green, OH
August 16-19 Lucas Oil NHRA Drag Racing Nationals in Brainerd, Minnesota
August (middle?) World of Outlaws Sprint Car Races in Knoxville, Iowa
August 17-19 Rolex Monterey Motorsports Reunion - Vintage Races featuring the Shelby Cobra at Laguna Seca Raceway in California
August 12 NASCAR road race at Watkins Glen, NY
August 19 NASCAR oval race in at Michigan International Spedway
August 25 NASCAR oval race in Bristol, Tennessee
August 11-12 TORC Offroad Race at Bark River, Michigan
August 17-19 Red Bull Indianapolis Grand Prix Motorcycle Racing at Indianapolis, Indiana
If you can't attend a national event go to a local dragway, oval dirt track, oval paved track, etc as they usually race at least once a week.
Other places of interest in the US
Niagara Falls, NY - Niagara Falls
Boston, Massachusetts - City, Harbor Fishing for stripped bass/blue fish,
Titusville, Florida - Kennedy Space Center (Take one of the tours)
Orlando, Florida - Many amusement parks, museums, attractions, etc
Seattle, Washington - City, Whale Watching, trip to Mount Rainer National Park (Stay at the top in the Paradise Inn)
Everett, Washington - Boeing Factory Tour
A National Park Service link that might be of interest to you:
http://www.nps.gov/findapark/index.htm
Thrill Rides-
Las Vegas, Nevada - Stratosphere Hotel -Skyjump, Insanity Ride, X-Scream and Big Shot