Marc Malkin

Jody Cortes / WENN

Pete Wentz and Barbra Streisand in the same room together!

What ever will they talk about?

Actually, there's an easy answer for that: gay marriage.

Wentz's band, Fall Out Boy, and Babs are just two of the boldfaced names expected at a Vote No on Prop 8 fundraiser Oct. 21 in Beverly Hills.

For those who haven't heard, Proposition 8 is a November ballot initiative that seeks to overturn California's legalization of gay marriage.

The upcoming benefit lists Streisand as its honorary chair, with Wentz and his crew as cochairs along with Rob and Michele Reiner and television wunderkind Greg Berlanti.

Steven Spielberg and Kate Capshaw are also chairs, as is Oscar-winning producer Bruce Cohen and his partner Gabe Catone, who were married by L.A. Mayor Antonio Villaraigosa in June.

The event, taking place at supermarket magnate Ron Burkle's Green Acres Estate, will also feature a performance by Melissa Etheridge. Ticket prices range from $1,000 to $250,000.

Spielberg and Capshaw recently made headlines by donating $100,000 to No on Prop. 8. Brad Pitt did the same, while Fall Out Boy and T.R. Knight gave $50,000 each.

Another celeb-filled No on Prop 8 benefit, Heroes & History Makers, takes place this Sunday, Oct. 12 at the Mondrian Hotel in L.A. Honorary hosts include Alan Cumming, Dana Delany, Nia Vardalos, Marissa Winokur, Chad Allen, Milk director Gus Van Sant and even Loni Anderson. Tickets start at $100.