Bolt Bus is a premium brand bus service operated by Greyhound which provides a twice daily service from the West Oakland BART Station taxi stand to Los Angeles' Union Station. These buses offer a similar experience to megabus; according to the website: wifi, more legroom, power outlets, and cheap tickets, but some first hand experience would be great to add.
From boltbus.com:
Stop is located inside the West Oakland BART Station where we utilize the taxi stand for loading/unloading. Parking is available on 5th Street between Chester St. and Mandela Pkwy for $5.50 per day on a space available basis.
1-877-BOLTBUS (1-877-265-8287)