Which domains are commonly found to mediate protein protein interaction? - (Sep/17/2013 )

I only know that WD40 and coiled coil are likely to mediate protein interactions by interacting with the same domain/motifs between two interacting proteins. Are there any other domain or motifs which often mediate PPI?

SH3 is famous. BH domains in Bcl-2 family are also extensively studied. They are present in some other non-apoptotic proteins too. Even on viral proteins. Nobody knows how they are developed.