Stan Lee has made cameo appearances in almost every Marvel Comics-based film made to date, and has now completed his cameo appearance for Iron Man, and is in planning for his appearance in The Incredible Hulk. In an interview with Forbes, Lee discussed his cameos.
I've already done my Iron Man cameo. I think you'll get a big kick out of it when you see it. They shot The Hulk I think in Toronto and other places and I wasn't able to fly there. But they said by the end of this month or the beginning of next month, they'll try to shoot a scene or so in Los Angeles so I can do a cameo, so I'm waiting expectantly.
Lee's cameo appearances go back at least as far as the first Fox X-Menmovie, and have continued through in most of the films based on Marvel comics since that time.
Iron Man, starring Robert Downey Jr., Terrence Howard, Jeff Bridges and Gwynth Paltrow flies into theatres on May 2, 2008. The Incredible Hulk, starring Edward Norton, William Hurt, Liv Tyler and Tim Roth arrives just a little over one month later, hitting the screen on June 13, 2008.