Santa Monica has two really good shops: Helen's Cycles carries a lot of high end bikes like Colnago, Pinarello, Seven, Cervelo, Look, Orbea, in addition to the more common Treks and Cannondales. They also have stores in Manhattan Beach and Arcadia, but those stores are tiny in comparison. Cynergy Cycles just opened a beautiful new store in SM also, carrying only Specialized and Bianchi.
While in town, you might also want to check out the Los Angeles Velodrome in Carson. They rent track bikes and give lessons -- sounds like fun!
http://lavelodrome.org/training.htm
Oh, and almost forgot... don't forget to purchase a copy of:
http://www.amazon.ca/Bicycle-Rides-L.../dp/0961915137
I believe there is an OC version as well, but I'm not sure.