Federer is pretty good at doubles, although I haven't seen him play that format myself. He has six titles, (almost got his seventh in Bangkok last year: he and Yves Allegro won the first set of the final but couldn't finish it off).
He doesn't play so much now that his singles career has er, blossomed, but has won TMS Miami (and other titles) with Max Mirnyi, and Gstaad with Marat Safin. He even played with Lleyton Hewitt at Wimbledon a few years ago, and they lost a 5 set thriller to Bjorkman and Rafter (who then defaulted - aargh).
You'll probably catch him playing doubles later in the year with Allegro if he decides to play Switzerland's second DC rubber; they usually enter a couple of ATP tournaments for "practice".