This weekend, when moviegoers watch slatternly educator Cameron Diaz try to seduce wealthy, nerdy substitute Justin Timberlake in the comedy 'Bad Teacher,' a lot of those viewers will be looking for a little extra spark of tension. After all, you don't have to follow celebrity gossip all that closely to know that, in real life, Diaz and Timberlake dated for nearly four years before breaking up in 2007. Why would they want to work together again? And how will their failed romance off-screen affect their chemistry on-screen?

It turns out that real-life exes reuniting in movies isn't all that rare. Whatever bitterness and hurt feelings may have attended the break-up, Hollywood stars tend to be pros who can set aside their stormy shared pasts and work together again amicably. In fact, sometimes viewers may wish there was more drama evident on-screen between some exes.

In the case of 'Bad Teacher,' director Jake Kasdan spoke to Entertainment Weekly's PopWatch blog during last year's shoot and said Diaz was enthusiastic about Timberlake's casting. "They're good friends, and they're both incredibly funny people," Kasdan said. "They have a shared sense of humor. It's easy for them to be funny together."

Below, we've compiled a list of some famous former couples who worked together again after their break-ups. Some of the results were classic films, some not-so-classic. If you see 'Bad Teacher' this weekend, come back and let us know which camp you think the Diaz-Timberlake reunion belongs in.