Why do these Ocean's 11 costars have such great chemistry on screen? Because of their real-life chumminess, naturally. At least they spend some of their time together giving back with their charity Not on Our Watch.

Vince Vaughn and Jon Favreau This pair of funnymen met on the set of Rudy, but after playing best buds in Swingers, the two have become frequent collaborators. (They're  teaming again in the upcoming Four Christmases.) What can we say, they're money.

Leonardo DiCaprio and Tobey MaguireThis bromance goes back to the duo's teen years, when they met on the set of Parenthood. It's nice (and rare) to see that both stars have remained friends as they each found their own success. 

Ben Affleck and Matt DamonThe original bromance teamed up on the Oscar-winning screenplay for Good Will Hunting and the hit Project Greenlight. With Matt a mega-star and Ben now working behind the camera, who knows what their next collabo will be

Will Ferrell and John C. Reilly After creating comedy magic in Talladega Nights (shake and bake!), this funny pair is went back to the well with writer/director Adam McKay in Step Brothers. See Bromances are like family!

Ben Stiller and Owen WilsonStiller cast Wilson in The Cable Guy, and the duo have since costarred in seven movies, including Zoolander, Starsky Hutch. Who says mixing work with relationships doesn't work

Lance Armstrong and Matthew McConaugheyArmstrong and McConaughey have bonded over their mutual passion for such sporty activities as biking, running and removing their shirts in public.

Ryan Seacrest and Simon CowellThese two may play enemies when the cameras are on, but don't think you're fooling anyone, guys. Personally, we think their front is cute. (Plus, we like to think this pairing inspired Seacrest to produce MTV's Bromance.)

Seth Rogen and Jonah HillThese laugh machines took their bromance to the next level by actually becoming twins. (Just look at them!) It seems their Superbad costar Michael Cera wants in on the fun, making us wonder: Do three-way bromances work

Tom Cruise and  Will Smith As two of Hollywood's biggest heavyweights, Cruise and Smith may be rivals when it comes to landing blockbuster roles, but there's nothing but love between these two BFFs (and  their respective wifeys).