How do I wirelessly stream my movies to my projector? I love using my Airport Express to wirelessly play my music.

I have a projector at home, and I would like to wirelessly play my movies, which were not downloaded with iTunes.

I was considering purchasing an AppleTV for this purpose. Do you think it is a good solution for my material which is not iTunes-related?
The streaming of music and video to Apple TV is quite remarkable in my book. Having Safari on the iPad, iPhone seeing the AppleTV as a target for many video types is still like magic to me.

Not everything streams, but if it's HTML5 video or something you don't mind placing under iTunes's purview - it's a great solution. As AirPlay gets more prevalent, the web sites that will allow this should grow over time. With media you control, it's ready to go with perhaps a re-encode if it's not something the Apple TV expects to play out of the gate.