I'll have to watch Go again as I haven't seen it for a while, and there were so many plot threads; I remember doubling over with laughter with the cat subtitles, and jumping at the same time as Katie Holmes' character when the gun goes off ("I'm alright!").
Mysterious Skin is quite difficult to watch in places, partly because the acting is so good, but definately worth it and the ending is one of my favourites of any film I've seen. Brick gets 5 start from me just for being one of the most original films I've seen for soooo long.
Fun is definately worth a watch, particularly if you're a fan of Thirteen, because they're quite similar. Fun is much more low-budget looking and some parts of it dont work, but I love it because (like Thirteen) it's not preechy and it avoids cliches which are so often par for the course in "troubled teen" flicks. It also doesn't try to come up with any easy answers.
I haven't seen Kids but I've been meaning to for some time.