Some off the top of my head: czapka (usually worn by lanciers), Pickelhaube (spiked Prussian helmet), bearskin (tall furry black hats worn by all those Royal Guards units), porkpie, straw, boater, fore and aft, tricorn, Phrygian cap, Liberty cap, titfer (Cockney rhyming slang for hat, "tit fer tat"), peaked hat, fatigue cap, ski cap, busby (worn by hussars, with a kolpak 'bag' on top), s(c)hako, turbin, snap brim, and fedora. Hope that helps, of troy.