Rafael Nadal

By far the Spaniard's best season ever, with Nadal winning his first non-clay court Slam at Wimbledon, taking his fourth straight crown at Roland Garros, winning the Olympic gold on hard courts and five other significant titles. While he was clearly worn down physically after Beijing and was forced to miss the Tennis Masters Cup and the Davis Cup final, no player scored as many impressive victories over his top rivals as Nadal did. His goals in 2009 should be to win a hard-court Slam, and his best chance will come in Australia, after his right knee has healed and he's had seven weeks of rest. The 22-year-old has improved his all-around game enough for a long stint at No. 1, but if the lefty doesn't schedule himself more carefully, he could run himself into the ground by age 26, a la Bjorn Borg. -- Matt Cronin