15 Celebrities Who Have Completed the Ice Bucket Challenge ...

The cast of Grey's Anatomy completed the challenge while on set! They challenged the cast of Scandal and the cast of the new ABC drama, How to Get Away with Murder. They're just some of the many celebrities who have completed the ice bucket challenge.

Britney was nominated by her sister to complete the challenge! She accepted and, in return, Spears nominated Adam Sandler, then-boyfriend David Lucado and close friend Robin Greenhill.

Anna Kendrick got nominated Brittany Snow and Catherine Giudici-Lowe, allowing her to "double donate" to the cause. She passed it on to Parks and Recreations' Aubrey Plaza, The Office's John Krasinski and Cat Deeley.

Arrow's Stephen Amell was nominated by Robbie Amell and even tried to one-up him by adding more ice in his bucket. Colton Haynes and Emily Bett Rickards, Stephen's co-stars, also took on the challenge.

J.Lo accepted the challenge and nominated Iggy Azalea and Pitbull, plus her BFF Leah Remini. Iggy accepted J.Lo's challenge and then passed it on T.I., Charli XCX, and Rita Ora (who completed the challenge on the streets of NYC).

Justin actually did the ice bucket challenge twice. The first time, he nominated President Barack Obama, Ellen DeGeneres and comedian Chris Delia. The second time, he told all of his fans to consider themselves nominated!

Taylor teamed up with Jaime King to complete the challenge AND donate to the cause.Taylor passed on the challenge to Selena Gomez, who then passed it on to James Franco!

Ryan was nominated by Bill Gates (um, WOW) and then nominated David Beckham.

Lena was challenged by Hart of Dixie's Jaime King and passed on the challenge to her fellow Girls co-stars, including Allison Williams.

Emma was nominated by BFF Taylor Swift. She completed the challenge and nominated her boyfriend, Andrew Garfield!

One Direction's Niall Horan was nominated by Brazilian soccer player Neymar and he took on the challenge while on tour! He also nominated fellow band member, Louis Tomlinson.

Jake Miller took on the challenge while on stage in NYC! He wasn't the only one who completed the challenge in New York. Disney Channel's Laura Marano accepted the challenge in Central Park!

Fifth Harmony was challenged by z100 and iHeartRadio and completed it while on tour! Tour-mate Shawn Mendes, who also completed the challenge, did the honor of dumping the water on them! They nominated Austin Mahone, and when their other tour-mates, The Vamps, were nominated, the girls were the ones to dump water on them! Fellow girl-group Little Mix also completed the challenge.

Lucy Hale, Sasha Pieterse, Ian Harding, Keegan Allen, and Ashley Benson all participated in the challenge! Some of them were even nominating each other, LOL! Ashley was nominated by Vanessa Hudgens and passed the challenge on to Emma Roberts, who then passed it on to most of her American Horror Story co-stars, including fiancé Evan Peters.

Demi Lovato completed the ice bucket challenge outside her New York City hotel with the help of some of her fans. She was doused with FIVE buckets of ice water and, in turn, passed on the nomination to five people. That included her little sister and her boyfriend, Wilmer Valderrama!

By now, SO many other celebrities have joined the fight to raise awareness to ALS. I think it's so awesome that they participated AND donated to the cause. If you haven't done so, do it now on alsa.org. Which celebrity did you love to see take on the ice bucket challenge? Who would you nominate?