Maybe it's unfair to pick out Lotro for inventory management, but it's the game I'm playing at the moment. Every session of play is either ended or started or interrupted by the need to vendor or port to my house or a trip back to town for banking and the auction house, but usually it's all of them to empty out the bags of every kind of junk:
1) Recipes: probably making the most demand on space, with metalsmith and tailoring patterns being particularly annoying. Yeah I complain when they also make the most money per slot in the inventory. But the whole mechanic of dropped recipes needs to go. Two solutions: make the normal dropped recipes a reward for unlocking mastery in a profession (there's no reward at all associated with it except unlocking more grind, and it would line up nicely with levelling), and all single use dropped recipes should be obtained from the crafting guilds and non-crit versions requring the small rep item or none, and the crit version requiring medium rep item.
A more radical solution for metalsmith/tailoring to cut down on the amount of scrolling in the recipe book and add some individuality is to restrict racial designs to that race, i.e. an elf makes elf clothes.
2) Potion/Salves: being able to use salves on yourself and others is a nice idea, but having the standard type as well, means I usually end up with a dozen different types only to vendor them. Keep only salves, simple as that! Conditions on a whole in Lotro are chaotic, unlike something like Guild Wars (previous game, sorry).
3) Reputation items: sooner or later they are going to have to introduce a special tab for those.
4) Yellow items: in a game where crafted items are more powerful, they are just vendor trash, maybe not at early levels but in the 40s they just don't seem to sell at all, and have gotten fed up with listing them.
5) Vendor trash: why the hell do they only stack to 10! But the whole concept of picking up bits of monsters and junk to make money in an rpg really needs to go. In a game with a decent crafting system why not create an economy where all money is obtained from gathering and crafting rather than picking up broken wings and insect legs. It's funny but when you think of how much money you make on your first visit to the barrow downs and I know I'm not the first to notice that, picking up bits of undead and rats and maggots and baraghest. Ughh!
That's enough for now, there's probably more to add to that list, but need to go organise some space on my alts.