"Comic Relief" (9 p.m., HBO): Whoopi Goldberg, Billy Crystal and Robin Williams join forces again to celebrate the 20th anniversary of "Comic Relief." This year's event, held in Las Vegas, benefits

"Comic Relief" (9 p.m., HBO): Whoopi Goldberg, Billy Crystal and Robin Williams join forces again to celebrate the 20th anniversary of "Comic Relief." This year's event, held in Las Vegas, benefits victims of Hurricane Katrina. The star-studded lineup includes George Lopez, Lewis Black, Roseanne Barr, Bill Maher and many others.