I loved the hot tub episode too. It was one of my favorites (when Jean-Paul jiggles the keys in front of the baby and says, "Mommy's little bastard.")
My two faves are the Jimmy episode (mainly for the last part, when Mel Torme sings "When You're Smiling" to Kramer at the mentally challenged adults banquet, which is my all-time favorite scene--if you watch real close, you can see Kramer actually start to crack up because the audience is laughing so hard and that's the only time I can remember when he did that), and the episode when Kramer builds the Merv Griffin set in his apartment ("El Paso? I spent a month there one night.")
I'm sure this question has been posted a millions times here, but I'm new and I was hoping someone would post it again.