Horse Races Now is a handy free app that can turn your iPhone into a complete racing program. After signing up for a free account, you can look at the racetrack info closest to you, or anywhere else in the US. The app features live streaming video, and race replays go back up to two years.
You can set your favorites up (tracks, horses, jockeys) and get push notifications of the latest results. A search engine provides access to info and replays from every North American track.