Jennifer Aniston turns 50 years old today, so naturally she hosted a huge birthday bash over the weekend in Los Angeles. Her party was filled with celebs including Katy Perry, Orlando Bloom, Reese Witherspoon, Laura Dern, Gwyneth Paltrow, John Mayer, Robert Downey Jr., Kate Hudson, Demi Moore, George and Amal Clooney, Courteney Cox, Barbra Streisand, and Lisa Kudrow.