According to various national and local reporters and now on MLBTR, the Reds just traded a package around Yonder Alonso for San Diego ace Mat Latos.
Latos is a tremendous pitcher, although it'll be interesting to see if he has any problems going from PETCO to the Little League field they have in Cincy. Looking at his splits on Fangraphs, he's done just as well with homers on the road as at home, so maybe Cincy isn't too worried.
EDIT: Troy Renck (@troyrenck) says the Padres are also getting Edinson Volquez.
EDIT #2: Grandal, Boxberger also going to SD.