George Clooney, Will Smith, and Gwyneth Paltrow will join an impressive list of stars taking part in tonight’s “Stand Up to Cancer” telethon airing on CBS, Showtime, and other broadcast and cable networks.

Other newly announced celebrities include Denzel Washington, Renée Zellweger, Kathy Bates, and Richard Branson. Kareem Abdul-Jabbar, Lance Armstrong, and Elizabeth Edwards were previously announced as participants.

Performers will include Green Day’s Billie Joe Armstrong, Neil Diamond, The Edge, Herbie Hancock, Lady Antebellum, and Leona Lewis.   Queen Latifah, Martina McBride, and Stevie Wonder were among those already announced.

Clooney in particular is a fundraising heavyweight. At the Emmy Awards on August 29th, he accepted the Bob Hope Humanitarian Award for efforts on behalf of victims of this year’s earthquake in Haiti, the 2004 tsunami in Indonesia, and the September 11th terrorist attacks.

“Stand Up to Cancer” is aimed at raising money to speed up innovative cancer research, according to movie producer Laura Ziskin (Spider-Man), who is a cancer survivor and co-founder of the Stand Up to Cancer group.

The telethon is returning for a second time after the 2008 event helped deliver more than $100 million for research.

This year’s telethon will be simulcast tonight, commercial-free, from 8pm to 9pm ET.

CBS’s own Katie Couric will act as one of the show hosts.

Donations can be made year-round through www.standup2cancer.org/survivor, and 100 percent of the contributions will go directly to cancer research.