Dragonskin armor that is generally available from magic shops. Also some barbarian armor (from Kree&shops iirc) and I think there were flame resistant robes. Not really worth it though, but dragonskin makes good early armor if you can afford it. Still for tech characters it's better to go with machined plate and arcane platemail or robes for magic characters. Also, I don't think fire resistance items will help with item damage that elementals etc. cause making them far less useful. Use dog to kill them if you go melee. For mages, gun/bow or throwing guys they shouldn't be any trouble as they are slow and easy to kite.
Lots of things will help you increase fire resistance, almost all armour has fire resistance for example. Some notable examples with high fire resistance are elite plate, the Iron Clan Armour (obtained at the end of the Iron Clan quest, small characters only), arcane robes (small and medium characters only), Robes of Fire Protection (obtained in Tulla, medium characters only), arcane rings, the Chill Shield and arcane shields. Some backgrounds, like the human-only Escaped Lunatic, give fire resistance as does the spell Shield of Protection (+45 at max aptitude). For a character with all round decent resistances arcane robes (EDIT - or red barbarian clothes), an arcane ring, a ring of protection, a dorian amulet or similar, the Screaming Shield and the Shield of Protection spell should have you mostly covered. Neutral or tech characters struggle to obtain the same levels of resistance a magickal character will do. EDIT: The NamelessOne has pipped me to the punch, as he mentioned dragon skin leather and red barbarian clothes are also good picks.