Male celebrities who starred together in film or television shows more than once...

[elegant20]

Those that appeared in film together and somehow starred in the same film, even they if didn't appear in any scenes at all or somehow did appear in the same scenes together.

Christopher Lloyd and Michael J. Fox in 3 Back To The Future movies, plus a guest spot in Spin City.

 

[montanaguy]

John Schneider and Tom Wopat: Dukes of Hazzard, Smallville, and made for tv movie "Christmas Comes To Willow Creek"

 

[Skull Mason]

corey haim and corey feldman in every movie in the 1980s

 

[elegant20]

Ironically, when Corey Feldman first met Haim, he didn't like him one bit and he thought he is too much of a sissy, but when he figured about the popularity that happened between the Corey mania, he realized the importance of it and that's how they became friends.

 

[cdollar]

Charlie Sheen and Jon Cryer (Hot Shots and Two and a half men)

 

[cjc3552]

Robert De Niro and Joe Pesci- Goodfellas and Casino
Robert De Niro and Al Pacino- Heat and Righteous Kill
Robert De Niro and Ben Stiller- Meet the Parents and Meet the Fockers
Robert De Niro and Billy Crystal- Analyze This and Analyze That

(Now my head hurts)