Lady Gaga tops Forbes’ celebrity 100 list, Oprah No 2

The men and women on our annual Celebrity 100 list — the most powerful people in the entertainment business this year — earned US$4.5 billion over the last 12 months by starring in films, playing basketball, walking the catwalk and more. But they also rose to the top by garnering influence.

These days that means mastering social media. Lady Gaga topples Oprah Winfrey from her No.1 spot on our list, which she’s given up for only the third time in seven years.

Gaga is there not just because of the US$90 million she earned with a monster tour, but also because of her 32 million Facebook fans and 9.5 million Twitter followers — aka Little Monsters — who helped move 1 million digital downloads of her recent single “Born This Way” in only five days. They’re also happy to buy the MAC makeup, Monster headphones and Virgin Mobile phones she features in her videos.

Oprah doesn’t fall far though. The daytime talk maven, who earned US$290 million last year, comes in second. Winfrey’s earnings sank US$25 million partially due to a reduced payday at SiriusXM. She still earns big from her syndicated show and from the stars she’s spawned, including Dr. Phil (No. 18) Rachael Ray and Dr. Oz. Winfrey’s earning power will take a bigger hit next year, when her syndicated show ends and she concentrates all her efforts on the struggling OWN network.

Maybe it would help if Oprah took a lesson from No. 3 Justin Bieber. The Biebs debuts on our list at the tender young age of 17, with US$53 million earned over the last 12 months thanks to concerts, music sales and a 3-D documentary movie that grossed US$100 million at the global box office. If this were 10 years ago Bieber would still be paying his dues in small clubs and schools, but thanks to the Internet, he’s a sensation. His first hit song, “Baby,” has been viewed 500 million times, a YouTube record.

Reality TV it girl Bethenny Frankel is another newbie worth noting. Famous for her newest hit show, Bethenny Ever After, she’s used the small-screen platform to promote her Skinnygirl brand, helping her earn US$55 million this year. She joins our list in 42nd place. Her entrepreneurial prowess — she sold her Skinnygirl Cocktails to Fortune Brands and nabbed a US$100 million cut of the deal paid out over multiple years — also put her on the cover of our magazine this week.

The Celebrity 100, which includes film and television actors, TV personalities, models, athletes, authors, musicians and comedians, is a measure of entertainment-related earnings and media visibility (exposure in print, television, radio and online). We also measure social media power by looking at each celebrity’s presence on Facebook and Twitter. The earnings consist of pretax income between May 1, 2010, and May 1, 2011. Management, agent and attorney fees are not deducted. Forbes has been publishing the list annually since 1999.

Despite problems on and off the golf course, Tiger Woods still makes the top 10, ranking sixth with US$75 million in annual earnings. Woods hasn’t won a tournament since the revelation of his marital infidelities in 2009, and he recently withdrew from The Players Championship. But he still commands US$3 million a pop for overseas appearances, and collects money from his remaining sponsors, Nike and Electronic Arts.

Having a much better year: Leonardo DiCaprio. The star makes the biggest leap on our list this year, rising from 71st place to 15th, thanks to two huge movies: Shutter Island and Inception. The latter earned US$825 million at the global box office, making it the sixth-highest-earning film of 2010. That went a long way toward helping DiCaprio earn US$77 million over the last 12 months.

Will Smith returns to our list this year thanks to the upcoming Men in Black III, in which he’ll reprise his role as Agent J. Smith had fallen off of our list in 2010 because he took time off to nurture the budding careers of his children, Jaden and Willow. Jaden starred in a remake of The Karate Kid (which Smith produced); the film earned US$360 million. Smith helped Willow with her hit song “Whip My Hair.” The video for the song has been viewed 11 million times.

Notable drop-offs include Britney Spears, who ranked sixth in 2010 but stumbled this year because she didn’t tour. With the Harry Potter franchise coming to an end, Daniel Radcliffe (who ranked 82nd last year) also failed to make the cut.

Dorothy Pomerantz, Forbes.com