Alicia Silverstone was originally offered the part of Valerie Malone on the 90210 cast but turned it down leaving the door open for Tiffani-Amber Thiessen.
Shannen Doherty was removed from the 90210 cast at the end of the fourth season because of consistently being late on the set and her constant conflicts with other cast members.
Brian Austin Green got some exposure the year before Beverly Hills 90210 began by doing Kellogs Corn Pops commercials.
Luke Perry got interested in acting as a child by watching soap operas with his mother. Eventually, he briefly appeared on a few episodes of the daytime drama "Another World".
The series finale (2 episodes on the same night) pulled huge audiences, especially in the last half-hour during Donna's Wedding but the show still was (barely) beat out by "Who Wants To Be A Millionaire".
(Posted by Stephen Strong)