[Belthan]

As far as standard items, a quick glance at the inventory for one of my complete-freak characters says Daedric Cuirass is the most expensive armour (4800 gold list price) and Daedric Warhammer is the most expensive weapon (5000 gold). As for enchanted items, the most expensive thing I've found so far is the Mundane Ring (list price a whopping 21600 gold) but there could be other items that are even more expensive that I haven't found yet.