We already heard from Donnie and Danny's interview with Faz.net that they are working with Timbaland. And according to the Thomas Crown Chronicles, the New Kids are also working Jim Beanz.
I thought I'd put together a list of people that have been rumored to be working on the album since the news has been spread out throughout this blog:
Rodney Jerkins (Darkchild)
Colby O' Donis
There may be more that I'm forgetting, so leave comment if I missed someone.