By People Staff
Updated August 17, 2009 12:00 AM
Credit: Michael Tran/FilmMagic; Todd Williamson/WireImage

It’s going to be a crowded ballroom for Dancing with the Stars’ ninth season. Sixteen celebrities — including Donny Osmond, Melissa Joan Hart and Aaron Carter — have signed on to do the cha cha and the paso doble on the ABC show, which premieres Monday, Sept. 21.

“When we increase the cast we find it makes the competition more interesting,” DWTS executive producer Conrad Green tells PEOPLE. “It was about trying to make it as big as possible and try to get that sense of fun and excitement and real character come through on the show.”

The sweet 16 lineup, which was announced live on Good Morning America Monday, also includes familiar faces like former Dallas Cowboy Michael Irvin, reality star Kelly Osbourne and supermodel-turned-billionaire businesswoman Kathy Ireland. Lesser-known celebrities, like snowboarder Louie Vito, Iron Chef‘s Mark Dacascos and model Joanna Krupa join the cast as well. But by far the most eyebrow-raising contestant is former House of Representatives Majority Leader Tom DeLay.

“He’s a fairly divisive figure in as much as Democrats will probably be hoping he fails and Republicans will probably be melting down the phones to keep him in,” Green admits. “I love that kind of level of engagement.”

Adds Green: “Tom loves dancing. He dances with his wife. He watches Dancing with the Stars religiously. For him it was a no brainer, but for us it was an absolute shock.”

Professional dancer/celebrity pairings will be announced on August 24, Green says, “because of geography, will be meeting their partners for the first time at various times throughout the week.”

The complete cast for Dancing Season Nine

Mya, singer Melissa Joan Hart, actress Michael Irvin, former Dallas Cowboy Ashley Hamilton, actor, comedian, singer-songwriter Aaron Carter, singer Kathy Ireland, former supermodel-turned-businesswoman Debi Mazar, actress Natalie Coughlin, U.S. Olympic swimmer Louie Vito, snowboarder Chuck Liddell, ultimate fighting champ Donny Osmond, singer Tom DeLay, former Republican congressman Macy Gray, singer Joanna Krupa, model and actress Mark Dacascos, Iron Chef personality Kelly Osbourne, reality star

–Monica Rizzo

Michael Tran/FilmMagic; Todd Williamson/WireImage