Jason Giambi has admitted it. He was juiced. That powerful physique? Created by chemicals. And who did he get the stuff from? Why, Barry Bonds' personal trainer, of course. In fact, his opening inquiry that led to the use of the steroids was to ask Bonds' trainer Greg Anderson "what are the things you're doing with Barry?" And while Anderson never came straight out and told Giambi that Bonds was doping as well, I think the circumstantial evidence against Bonds is even more damning that it was before.
UPDATE: Turns out Barry has admitted (though he claims it was all a misunderstanding) that he was on the juice too. Which came out before I could get the above posted. Dang it!