For as long as I can remember, apple.com/trailers has been a great, ad-free place to see all the latest movie trailers in the one of the best video formats available on (and off) the web. During my ceaseless tinkering, I just noticed that Apple has created a sub-page at apple.com/trailers/iphone specifically for the iPhone, offering access to what looks like the same content and trailers you can view with a regular computer browser. In fact, visiting that URL in any desktop browser, including Safari 3 beta, redirects to the main /trailers/ site, ensuring that visitors don't get mixed up with the wrong page.
Perhaps even cooler, selecting a trailer on the iPhone reveals a page with a static picture where the trailer would be, and a play icon. Clicking this icon appears to take the user to an iPod-like app, where the trailer begins to buffer, and all movie controls are available. As icing on the cake, if you're already listening to media in the iPod app, your music/podcast will gracefully fade out, giving the trailer you want to watch full priority until you exit the movie.