George Clooney lobbies for Darfur and Reese Witherspoon advocates for breast cancer research. Brad Pitt stumps for rebuilding New Orleans while his longtime partner Angelina Jolie travels on behalf of refugees.
Then there's U2 frontman Bono, who is perhaps the world's biggest celebrity philanthropist with his longtime work on behalf of debt relief, trade and AIDS in Africa.
These days, it seems nearly every celebrity has a pet cause, using their fame and deep pockets to help the poor, oppressed and downtrodden.
It's the kind of work that has been central to the religious community for thousands of years. And religious people are actually the nation's most generous donors, according to Syracuse University professor Arthur C. Brooks.
Brooks has crunched the numbers and concluded that Americans who regularly attend religious services make up 33 percent of the population but contribute 52 percent of charitable donations and 45 percent of volunteer time volunteered.
So it would seem natural for the two sides to be working hand-in-hand. Yet many celebrities venture off on their own. Why the divide?
It can be summed up in two words: mutual suspicion.
Some conservatives point to this season's installment of "American Idol'"s "Idol Gives Back" telethon as an example. It raised at least $22 million for clean water, malaria prevention and housing for those in extreme poverty.
Conservative groups such as the Family Research Council and the American Life League took issue with some of the six charities chosen as beneficiaries of the telethon, saying some of the groups work in alliance with Planned Parenthood International or other groups that support abortion.
"If the show prompts your family to give, consider donating to an organization that shares your values -- not one that masks its radical agenda," the FRC cautioned in a newsletter. Idol Gives Back declined requests for an interview.
Some religious groups also question the accountability of some secular charities. Rocker Sting's charity, the Rainforest Foundation, is currently under fire from watchdog groups for delivering just 41 percent of donations to the cause.
Katie McNerney of the Washington-based Endeavor Group works behind the scenes to ensure her big-name clients know where there money (and reputation) is going. "These people get approached all the time by (non-governmental organizations)," says McNerney, "and they don't have time to do due diligence."
The firm, which advises singer Wycliff Jean and other luminaries, does the research, making sure the charity is legitimate and efficient. Then they strategize to make effective use of the client's money, time, and influence. "They expect a return on their investment," she said.
Yet the one thing celebrities have that many religious groups don't is just that: celebrity. And influence, perhaps more than time or money, is the biggest contribution the stars make.
A few words from the spotlight can raise more awareness than weeks of paid advertising, and the stars know it. Actor Ryan Phillippe wears charity T-shirts so paparazzi photos carry his message to the tabloids. Jolie deftly turns media fascination about the family she shares with Pitt into a platform for discussing the needs of refugees.
Simply raising awareness was one of the goals of Idol Gives Back, said executive producer Nigel Lythgoe. "It's trying to inform and educate an audience that they should be doing this. Not because we ask. They should be doing it," he told reporters before the telethon.
Bono has set the standard for raising awareness -- and then motivating people to act, observers say. He's been especially successful in getting the A-list Hollywood set to join in, and in recruiting alliances in the religious community.
"We work with people in a way that ... really lets people get into the meat of an issue. These issues are complex," says Kathy McKiernan, a spokeswoman for Bono's One Campaign.
"The people that we brought to Africa -- Brad Pitt, Matt Damon, Ben Affleck, Tom Brady -- we want to show them how the programs we advocate for are working. We take them to a Global Fund clinic. ... We'll take them to a school, in Tanzania for example, where kids are in school now because of debt relief. We make sure they have a chance to talk to Africans who are fighting against these problems. To hear from them what's working, what's not working. It's a really great opportunity for them to learn and to educate themselves."
Bono, who has described himself as a "not-practicing-enough Christian," has forged alliances with politicians, celebrities and religious leaders of all faiths, from "Purpose-Driven Life" pastor Rick Warren to progressive Christian activist Jim Wallis to the Dalai Lama.
McNerney said one thing Bono and the One Campaign have learned is to focus on common ground and leave political or religious ideology aside. Citing Idol Gives Back as an example, she said people who aren't sure where their dollars are going can still earmark it for a specific worthy cause, such as the group Malaria No More.
"In the end, it's about making sure bed nets get into the hands of people who need them and save their lives," she said. It's something everyone can agree on -- both generous religious folk and "people who don't go to church but who want to get engaged."