Gran is the town Blacksmith sells the two highest level item sets available to you that have no stat modifiers on them. These are comparably cheap to Chung's items, but are really only beneficial at the beginning of the game when you don't have much money and out-level gear relatively quickly. New item sets become available every 5 levels. e.g. 6, 11, 16, etc.
Susanthe town witch owns the potions shop and also sells town portal scrolls and items for composing. She doesn't always sell items for composing, and when she does the crystals/stones she sells are random. Every new act she adds better potions to her inventory for purchase. She's also the NPC that is used for compositions. Refer to the compose section for more information.
Chung sells the highest level item set available to you with composed stats already on the items, but still have their normal number of composes left. This means the stats on his items are bonus stats, giving them the potential to be the best items in the game (except for blue/gold quality items). Although his items are expensive they're well worth the investment, and are actually cheaper than trying to make the same item with the same stats yourself.
Paul from Chapter III, Paul (who lives in the South-West) gives you access to his 5x8 storage container. This gives you a place to store any items you don't need to carry around on you. This can be very useful when collecting centaur horns, for example.