What comeback Collabo's do you want to see?

I was thinking of people that have fallen off or are on their way off. I'm more R&B so... Here are my picks for collabs that would make people pay attention again:
Remix of Feedback by Janet Jackson featuring Ciara.
Monica and Kelly Rowland doing something ala "Same Script Different Cast"
Ja Rule needs to team back up with Lil Mo for a hit.
Alicia Keys and Lauryn Hill - Keys on piano and Hill on Guitar!
Justin Timberlake and Usher would be A MAJOR EVENT.
Fantasia and John Legend would be incredible doing Secret Lovers.
Chris Brown and Mario should do "The Girl Is Mine" by Michael Jackson and Paul McCartney.
My Supersong (ie: Missing You from Set It Off) would be: Beyonce, Tamia, Mariah, Syeesha (AI). They should do a big sister-girl anthem.
What are your picks?