As always, all eyes will be on the men's 100-meter dash, and this could be one of the best fields ever, with world-record holder Usain Bolt and former record holder Asafa Powell facing U.S.-record holder Tyson Gay. The 110-meter hurdles should draw plenty of attention, too. China's Liu Xiang is the reigning Olympic and world champion, making him his nation's best chance for a gold medal on the track.

With a star-laden roster that includes Kobe Bryant, LeBron James and Carmelo Anthony, the U.S. is the heavy favorite to bring home the gold. But the Americans haven't finished higher than third in a major international tournament since they swept to the gold in Sydney in 2000. They could face their toughest competition from Spain, which won the 2006 world championship.

The U.S. looks for an unprecedented fourth consecutive gold medal, led by three-time Olympian Lisa Leslie. Standing in the Americans' way is reigning world champion Australia and WNBA MVP Lauren Jackson. Other medal threats include Russia, which features American Becky Hammon on its roster, and host China.

Boxing strives to erase its tawdry image with a revamped scoring system and roster of new judges. Traditional powers Russia and Cuba send strong teams again. Light flyweight Zou Shiming is a strong favorite for China's first boxing gold. Demetrius Andrade and Rau'shee Warren lead a U.S. squad hoping to rebound after winning just one gold in the past two Olympics.

The U.S. men's chances plummeted when defending all-around gold medalist Paul Hamm injured his hand in May and could not fully recover in time for Beijing. China is the overwhelming favorite for gold after winning seven of the last eight world titles. Hamm's withdrawal clears the way for two-time world champion Yang Wei of China in the all-around.

American women are co-favorites with China for the team gold, and U.S. teenagers Shawn Johnson, the current world champ, and Nastia Liukin are threats for all-around gold. Their biggest competition should come from the Chinese, who have been dogged by questions that some of their girls -- including uneven bars star He Kexin -- don't meet the age requirement (16 in the Olympic year).

Defending champion Argentina arrives with a team confident after having won last year's Under-20 World Cup and with the added boost of FC Barcelona's Lionel Messi. Seven members of the U.S. team come from the squad that reached the quarterfinals of last year's U-20 World Cup. It is bolstered by Brian McBride, second all-time leading scorer for the American senior team.

The defending champion U.S. women must overcome the loss of forward and leading goal scorer Abby Wambach, who broke her left leg in an exhibition match against fellow gold favorite Brazil on July 13. Germany has won the past two World Cups.

The United States is seeking its fourth consecutive gold medal in what will be softball's fourth and final Olympic appearance until 2016 -- if then. The U.S. dominated four years ago in Athens, going 9-0 and winning by a combined 51-1. With 10 players returning from that squad, the Americans are heavy favorites but will be challenged by Japan, Australia and Canada.

Competition will be at futuristic-looking Water Cube, where ultrathin plastic stretches over a steel framework to form 3,000 translucent air bubbles. Michael Phelps tries to win eight gold medals and surpass Mark Spitz's record of seven golds from the 1972 Munich Olympics. The United States and Australia compete to finish on top of the medal standings.

The United States appears to lack the signature stars (Rulon Gardner, Cael Sanderson) of the past two Olympics. Russia is so strong, it must choose between former Olympic champions and world champions at some weight classes. Japan is the power on the women's side, with the potential to win multiple gold medals.