One of the cool things about D&D, and probably why it's survived so long, is that you can tinker with different subsystems without breaking the whole. Classes, for example, are a lot easier to plug-in or cut out than reshaping a whole skill system. Septimbrini called these parts you can fiddle with Building Blocks (I first heard of this at Jeff's). The traditional magic items are great examples, and they've been that way from the beginning. I've been trying to spotlight how within the building block of magic items are sub-blocks that serve different functions-- have done potions and rings so far. I thought I might pull back a little and think about the whole field.
I don't know why I put scrolls for charges/self, that seems wrong now, and there must be some room for exploration there.
I think most, if not all, of the magic apparel would fall with the rings. I think the wands can be broken down into two types, at least, the spell guns and the dowsing rods. I'm thinking about doing a one-page on the latter because they are pretty easy to define and describe-- detect enemies, magic, gold etc. I'm not sure I can come up with 20 different types though.
These simple categories aren't the whole picture. In looking at potions, I realized they existed to be short-term dungeon tools, too. Potions provide a toolbox that gives players choices in how to approach dungeon hazard/obstacles. And rings, because of their always on nature, turn out to be good defensive items, defending even when the wearer isn't prepared (feather fall).
I really like examining the magic items like this because it's possible we might discover another type of magic item that hasn't really been used to its potential. Also, If we're clearer about what makes the types unique we might be able to invent new items along those lines (like my idea of a ring of Force, though I'd be happy with a clearer name).