The Episode of Truth (see what I did there)

[queenoftheDales]

For the group as a whole it would have an A Plot (Penny and Sheldon) and a B Plot (Howard, Leonard, and Raj)
Pancake Batter
Adhesive Duck
Vegas

There is just something about these episodes that make me happy. I'll have to get back to you on individual episodes for the characters.

I was going to say Pancake Batter or Adhesive Duck as an example to present to JP . In these episodes, I like how JP manages to expands Sheldon some without falling completely out of character. (These are all S2-S3 episodes, so I think it's safe to say that the character traits are pretty solid by now).

Terminator Decoupling is a good one too. I'm not 100 percent sure that episode had a definite A/B plot, but it's still a good group episode. I much prefer the Leonard/Raj/Howard grouping. It seems like JG doesn't oversell the "nervous nice guy" crap when his character isn't dealing with a woman and he is so much more tolerable on screen.