Yeah, a few haven't aired yet but I have the DVD, so I've seen all of it. I have to say, the last part of Season 4 was pretty good.
Shell of a Man
The Lost Matress
Krabs vs. Plankton
Have You Seen This Snail?
Krusty Towers
Wishing You Well (this and the one above it are my personal fav. Of the season)
Squidtastic Voyage
Best Day Ever
The Gift of Gum
Driven to Tears
(And the ones that haven't aired yet...)
Born to be Wild
So that's my best of. I thought Season 4 had some more creative plots, but lost the same feel and perfect jokes that Season 3 had. Also, did anyone find it weird for Nick to show Season 5 episodes before Season 4 was completely aired?