IGN is reporting that the first trailer for The Green Hornet is going to debut on Jimmy Kimmel Live, Monday June 21. Seth Rogen, who plays the Green Hornet in the film, is going to be on Kimmel's show that night and is also going to introduce the trailer.
Also, it looks like the teaser poster for The Green Hornet that's currently being displayed on the floor of the Licensing International Expo in Las Vegas is in fact not the poster.
Sony informed IGN that The Green Hornet banners being used "were made by the Licensing Expo using official assets for the film, but that the banner seen featuring Rogen in costume is not the official film poster (which is still forthcoming). Also any footage being shown at the Expo is not the official trailer for the film, either."