Lucille Bluth plays a drinking contest against Kitty to win George Sr. back. She begins the drinking contest by grabbing a drink from a passing waiter, downing it in one go, and saying "That one didn't count." The entire time, she's sipping a glass of wine between turns, and she still manages to drink Kitty under the table. She gets a standing ovation for her one-liner at the end:
Waiter: Can I get you anything else, ma'am? Lucille: No, thanks. I have to get back to rehab.
GOB successfully disappearing (read: sinking) the family yacht, restoring his reputation as a great magician and getting rid of some bad evidence against George Sr.
Another one for GOB—after having spent all of "Best Man for the GOB" being manipulated by George Sr., he finally builds up the guts to ignore him, turning off the TV George Sr. was appearing on live from jail in defiance.
In the season three finale, the moment George-Michael becomes a man: by giving his uncle GOB a much-deserved black-eye for dating his girlfriend.
And doing the same to his dad in the season four finale—more awesome, this time, because it's what makes him finally get fed up with Michael after all the bullshit he's put him through for the past ten years.
J. Walter Weatherman, both times he appears. It's no coincidence that these two episodes together are Mitch Hurwitz's own favorites of the show.
Barry, when he realizes that the satellite photos of Iraq are actually a closeup photo of a man's balls. After several episodes of incompetence, it was nice to see him finally get a victory.
Buster in "Making a Stand." After the Gambit Pileup between Michael, Gob, and George Sr., it's Buster who gets the last laugh.
Ann, after enduring so much crummy treatment from her old flames, GOB and Tony Wonder, manages to trick them into sleeping with each other.
The making of season four. The sheer amount of effort to create such an intricate, multi-layered story and still make it all funny is mind-boggling.
There's something dearly satisfying about Michael finally letting loose on GOB near the end of "The Righteous Brothers" after having to put up with his antics for so long.