The title says it all! I've based my list primarily off of which episodes I most frequently return to.

(In no particular order)

-The Cincinatti Kids (Season 5)
-Confessions, Confessions (Season 2)
-The Fender Benders (Season 3)
-My Sister, Benedict Arnold (Season 3)
-The Big Bet (Season 3)
-Our Son, The Man (Season 2)
-Alice's September Song (Season 2)
-Cyrano de Brady (Season 4)
-Greg's Triangle (Season 4)
-Sergeant Emma (Season 3)
-Will the Real Jan Brady Please Stand Up? (Season 2)
-Is There a Doctor in the House? (Season 1)
-Peter and the Wolf (Season 5)
-My Brother's Keeper (Season 5)
-Two Petes in a Pod (Season 5)

"Every Boy Does It Once" - (Season 1)
"The Dropout" - (Season 2)
"A Fistful of Reasons" - (Season 2)
"Our Son, the Man" - (Season 2)
"The Winner" - (Season 2)
"The Wheeler-Dealer" - (Season 3)
"Her Sister's Shadow" - (Season 3)
"The Not-So-Rose-Colored Glasses" - (Season 3)
"The Big Bet" - (Season 3)
"Jan, the Only Child" - (Season 4)
"Everyone Can't Be George Washington" - (Season 4)
"Greg Gets Grounded" - (Season 4)
"Bobby's Hero" - (Season 4)
"How to Succeed in Business?" - (Season 4)
"My Brother's Keeper" - (Season 5)