As well as the case of Ben Johson, it is better known the case of Marion Jones, who in october 2007 admitted to had taken steroids after the Olympic Games of 2000. At first, he laid to the press and to the police saying that she never had taken prohibited substances. For this fact she lost her five medals and was punished with two-year suspension from her sports activities.
In the past year there were lots of doping cases during and after the Tour de France. For example, Rasmussen, the race leader, was pulled from the race by the governing body of his team, because he had lied them about his pre-training and because he had missed two doping controls during the race. A Spanish cyclist, Mayo, was caught in doping after the Tour, too.
I've found other doping cases in basketball, skying, football, baseball, skating, rugby...