You can book round - the world tickets on Delta (
SkyTeam) for 180,000 miles in
economy and 280,000 miles in
business class, United (Star Alliance) for 180,000 miles in
economy and 260,000 miles in
business class,
and American Airlines (oneworld) for 100,000 - 160,000 miles in
economy and 180,000 - 330,000 miles in
business class (exact number depends on miles flown).