Other runners taking part included celebrity chef Gordon Ramsay, who ran his 10th marathon, as well as Major Phil Packer, a paraplegic who was injured in a rocket attack in the Iraqi city of Basra last year.
Price, running for children's charity Vision, crossed the line with husband Peter Andre in a time of 7 hours and 11 minutes.
Ramsay, who was raising cash for the Scottish Spina Bifida Association, completed the run in just over four hours and declared it "the hardest race yet".
"It was so hot out there but there was amazing support."
Boyzone's Ronan Keating, running in aid of Cancer Research UK, confessed: "It hurt the whole way round. I'm not really a mileage runner... but it's great to come out and do this."
His bandmate - an emotional Keith Duffy - described the race as an "amazing experience" after finishing in three hours and 52 minutes as he raised cash for children with autism.
"The crowd were great. Moments come and you can't go any further but the crowd just keep you going."
Maj Packer hopes to complete the event in 13 days and is aiming to raise £1m for the charity Help The Heroes.
Meet Wonderwoman and Stig as they take on the London Marathon
He is running the race on crutches and is aiming to complete two miles a day.
Nell McAndrew was the first celebrity to cross the line, recording a time of 3 hours, 10 minutes and 20 seconds.
The model, raising cash for Cancer Research UK, said: "I can't believe it. It's nice to have a woman win the title this year."
Olympic badminton silver medallist Gail Emms was all smiles when finishing 37 minutes later.
But she added: "I tired a little bit at 15 miles and then got cramp at 18 miles. My legs have just seized up. I'm still in pain and I've forgotten the whole route."
Olympic gold medal-winning cyclist Chris Boardman, running for the National Autistic Society, described the experience as "horrible".
"Towards the last three or four miles I just couldn't care less. I just wanted somebody to shoot me but since they wouldn't I had to keep going," he said.
Former model Katie Price was hampered by a knee injury
A St John Ambulance spokesman said 6,038 runners sought medical help during the race, along with 128 spectators. Sixty-eight people were taken to hospital for treatment.
British runner Paula Radcliffe did not take part because of a broken toe, leaving reigning champion Irina Mikitenko to successfully defend the women's title.
Yamauchi came second, with Russian Liliya Shobukhova in third place.
Kenyan runner Sammy Wanjiru won the men's title after defending champion and fellow Kenyan Martin Lel had to withdraw on Saturday after suffering a hip injury.
Among the fun-runners was Postman Paul Simons, 45, from Edgware, north London.
He ran the fastest-ever marathon by a man dressed as Santa Claus in two hours, 55 minutes and 50 seconds, in aid of premature baby charity Bliss.
Mayor of London Boris Johnson had earlier reassured the public the marathon route would not be altered to accommodate an ongoing protest by Sri Lankan Tamils outside Parliament.
The occasion is crucially important for charities and organisers say it is the largest single fundraising event in the world.
Last year runners raised more than £46m for charity.
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It hurt the whole way round - but it's great to come out and do this
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