The ride from Pasadena to LAX will become even easier next year when the Expo line bike path opens (tentatively around August 2011). There will be a continous bike lane or path basically from Downtown LA all the way to LAX.

Downtown to USC via Hoover (marked bike lane).
USC to Culver City via Expo line (sparated bike path)
Culvery City to Lincoln Blvd via Ballona Creek (separate bike path)
Lincoln Blvd to In-N-Out via Lincoln and Westchester (marked bike lane)