treetoonI've always thought hats were really annoying, but I realized that actually I don't mind the ones that fit the TF2 universe which is set in the 60's during the nuclear age and cold war. It's a dark comedy sharing extreme similarities to the film Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb. Soldier's stash is a great example of an acceptable hat whereas pirate related hats and cosmetics like the Fairy Wings for heavy is I think when people had enough.
90% of the cosmetics are garbage, but some are actually alright; medals for example. I realize this is purely for FPS but it'd be interesting to see a version that catered to the original style of the game.
i can see this getting rather subjective at times (what counts as fitting the art style and what doesn't), so for more custom builds (is that the right word?) like this i recommend learning how to modify the vpk yourself, it's quite simple actually.
http://www.teamfortress.tv/16179/no-hats-mod/?page=5#141 is a great starting point