Clara Hughes is probably the only American to medal in both summer and winter Olympics, but I know a few others have, too - speedskaters and Nordic skiiers from Germany/East Germany and Eastern Europe/Soviet Union who also bicycled. Most of them medaled in the team cycling events. Eric Heiden (USA speedskating medalist) also qualified for the summer Olympics as a cyclist after his speedskating golds, but finished too far back to make the podium.