4.) Valerie Malone (Beverly Hills, 90210) - Aaron Spelling is known for his memorable bad girls: Heather Locklear on Melrose Place, Joan Collins on Dynasty. What made Valerie so deliciously bad is that she was played by former Saved by the Bell sweetheart Tiffani Thiessen. Just like that, Zack's one true love went from chaste kisses to conniving, lying and rolling a joint her first night in the all-American Walsh clan house. Sure, all that seems innocent now, but in casting against type and a long-lasting feud with Kelly Taylor (played by good friend Jennie Garth), Thiessen's nice girl ways revealed some sharply manicured claws.