Megan Fox

Before becoming a very big star with roles in the Transformers and Teenage Mutant Ninja Turtles series, Megan Fox, was an uncredited cast of Bad Boys II playing the stars-and-stripes bikini kid dancing under a waterfall in 2003.

She also appeared as Carla in Confessions of a Teenage Drama Queen in 2004 before bagging the most coveted role as Mikaela Banes in Transformers released in 2007.

Tom Cruise

I was always amused at cameo appearances and notable extras in movies who become superstar celebrities later on.

Tom Cruise has been receiving $25,000,000 for every movie like "The Last Samurai" and "Minority Report". He appeared on several movies before becoming the superstar celebrity he is now. One of his first movie appearance is as Billy in the Brooke Shield movie "Endless Love" in 1981.