The Big Bang Theory Season 3 Episode 11 - The Mate...
Leonard's mother (Christine Baranski) visits, which pleases Sheldon but upsets Leonard. .
The Big Bang Theory Season 3 Episode 10 - The Gori...
Sheldon attempts to help Penny understand Leonard's work, and Wolowitz becomes jealous when Leonard starts hanging out with his new girlfriend.

The Big Bang Theory Season 3 Episode 9 - The Venge...
Barry Kripke embarrasses Sheldon on NPR, and the gang rallies to help him get his revenge. Wolowitz, desperate to keep his romance with Bernadette alive, gets advice from a fantasy version of Katee Sackhoff.
The Big Bang Theory Season 3 Episode 7 - The Guita...
A squabble between Leonard and Penny sees Sheldon playing mediator, though out of his own incovenience from the sitiation rather than altruism.

The Big Bang Theory Season 2 Episode 19 - The Dead...
Penny feels threatened when another sexy woman moves into the apartment building.