We happened to be on vacation in California the week of the Red Bull Air Race in San Diego. Thankfully, our itinerary already included 2 days in San Diego, and the entire family was interested in seeing the race instead of going to the Wild Animal Park.
We even got to see it for free! You could buy tickets to watch it from the Embarcadero, but we went to Seaport Village and found a spot near a fountain where we could see the entire course! It was absolutely incredible. These guys fly at 300+ MPH and have to do very tight maneuvering in a timed course.
We could only see the Pre-Qualifying runs, since we had to start driving back the next day, but it was one of the best, cheapest events of our vacation!
UPDATE: I've made a public album of race pics here.