Ne-Yo has revealed that he was approached by the Spice Girls right before their comeback tour to write some tracks for their Greatest Hits album. Unfortunately and fortunately (depending how you look at it) he turned them down in order to work with Rihanna.
He says, "The Spice Girls asked me to write some songs but I couldn't find the time. They wanted something for their comeback album but I never got round to getting it done. I was recording songs for Rihanna at the time."
Rihanna was definitely a better choice for Ne-Yo. The Spice Girls only had temporary publicity but Rihanna is super hot right now and will be for some time.