The coolest green cars since Steve McQueen's Mustang will be on display at the sixth annual AltCar Expo, where attendees can ride in, test-drive and purchase alternative-fuel vehicles. Highlights include the Nissan Leaf, Toyota's plug-in Prius, the Chevy Volt and the Mercedes B-Class F-Cell. Santa Monica Civic Auditorium, 1855 Main St., Santa Monica. 10 a.m.-5 p.m. Fri.-Sat. Free. (310) 390-2930. http://www.altcarexpo.com.