My remaining three are official art portfolio books, that I bought at my university bookstore in the art section. I bought them all from the brand Itoya, and they all have 24 sleeves and are more expensive for much fewer sleeves, at about $10 to $20 each.
And of course the next size up would probably be my posters, but for those I just frame them up and display them on my walls or sadly roll them up into a poster tube.
Some people would rather store photocards in binders like collecting trading cards, but that seems too complicated for me and I'd be too inclined to collect every photocard from each album to complete the sets. Also because photocards come in so many dimensions, it'd seem too difficult to find sleeves tailored for each one. I've settled on my method with these art portfolio books, but I just recently ran out of room in my 4" x 6" book and have photocards waiting to be put in sleeves...maybe I will try the binder method some day, just for the smaller photocards, and have the larger cards in these books. The only downfall about the way I organize my cards, however, is if I get a new photocard and have to change the order of my cards, since the sleeves can't be moved like binder sleeves.