My favorite is the knitted/fulled Tricorn Hat at knitlikeapirate.com. First of all, how awesome is a site devoted just to piratical knitting? And second of all, I only like to make really useful things and a knitted tricorn hat has to be at the top of that list.
And here’s a collection of funky hats from the 60s (PDF). Those of you who were around back then, would you have worn hats like these?
The last one is a Sock Monkey Hat from Knitty.com.