In light of current trading and inventory systems, following enhancements to the inventory would be great.
1) Have different sorting options: by type, by price (stack or single item), by weight (stack or single item)
2) Have ability to show item value/weight ratio. Essentially, how much is 1lb of the item valuable.
This would greatly help when deciding if item is enough valuable to carry or is better to put in stash, due to it being too heavy for its price. Also, have sorting option for this. Currently, player is forced to get this estimation manually, on their own, which adds unnecessary tedium.