Fall Out Boy did a recent interview w/ Billboard- in that interview Pete Wentz stated there are no guests on the new album tracks (so far?) but at the top of his wishlist, he'd want Rihanna.
Wentz says it's been interesting to see how a group of friends and musical collaborators can "approach the same craft from a completely different perspective. When you've been doing this for 15 years with the same guys it's hard to find something fresh.