If you are using a Mac you can turn on Mac OS X's web sharing and stream (locally) almost any iTunes video that you want to the iPad (you don't need Air Video or StreamToMe or any third-party utility/app). However, the video must be in a format that is supported by the iPad.
This does require some simple preparation on the Mac (you need to make links to the directories that contain the videos) but frankly the quality is better than either Air Video or StreamToMe (because the video isn't converted, it's streamed directly from the original files). Air Video and StreamToMe have their own uses, but if you just need to stream some iTunes content over your local network I'd suggest setting up web sharing.
Here is a link that discusses this technique:
http://www.macobserver.com/tmo/answers/streamvideos_and_music_from_your_mac_to_your_iphone_oripad/