Off the top of my head:
*The scene from the "Model Students" episode involving Jessie's photoshoot on top of the stairs in the school hallway. Jessie is dressed like a hot schoolmarm and the photographer instructs Jessie to toss her glasses off and let her hair down for the wind machine.

*The "Substitute" episode in which that New York-ish actress Vicki that the boys hire to seduce that studly substitute teacher, Mr. Crane (although, she accidentally seduces Mr. Belding instead) that the girls are crushing on. Maybe a lot of it has to due with Bess Meyer's sexy legs and overall cute, albeit bumbling demeanor.

*That hot maid in the "Mystery Weekend" episode.

*Anything involving Nurse Jennifer (Nancy Valen), especially the scene towards the end when she seduces/scares straight/pranks Zack.