There was a very brief moment in American History X, where the kid tickles his sister's feet, it's a one stroke kind of thing though. Also, you might try Asteroid part 1? I can't remember, but there was a movie about an asteroid that had a fairly long scene with a guy tickling a girl's ribs I believe. Ferris Bueller's Day Off, one of the greatest movies ever made, has a tickling scene, but you can't see it, you can only see Mia Sara reacting to a tickling. However, I did read somewhere that Mia said that Mathew Broderick had to tickle her feet to get her to laugh, so the actress was not acting. Sorry I couldn't be of more help, but American History X and Ferris Bueller are good movies that I'd recommend to anyone, the tickling scenes are not the longest though.