Store everything according to Rings & Things' stock #'s, of course! 'cause you buy everything from us, right?

ok, more seriously...
I would break things down into categories like you just mentioned (Findings, Seed Beads, Metal Beads, Large Hole Beads, ... whatever seems to make sense and be manageble size categories). Maybe 1 Excel file per big category, and then use different pages inside each file, for subcategories.
To make re-ordering easy, you could subdivide them by who you buy them from, and then sort by their stock #.
Or you could have things alphabetical, still with a field for stock. When I had inventory sheets for goods that I was making things out of, I also kept 2 fields with cost (1 was the re-order cost per 100, GR, etc., the other was the cost per piece), to make it easier to calculate price of finished goods without flipping through catalogs.
The easiest alphabetical method (for finding things again later) is to name things somewhat like so:
<B>Broad category, Material, More Desc, Size</B>
Bead, Wood, Fancy 3mm
Bead, Wood, Plain 4mm
Bead, Glass, Firepolish, 4mm, Emerald
Bead, Glass, Firepolish, 4mm, Ruby
Bead, Glass, Firepolish, 4mm, Ruby AB
Ear Wire, Sterling, French Hook
Earring Post, Surgical, Drop-Style, 3mm, Yellow
Earring Post, Surgical, Drop-Style, 3mm, White
That way, things sort decently together.
And if you add new items at the bottom, you should be able to get them to re-sort properly. With things named like this, you coudl probably have them all in 1 big Excel file.
Another note ... always save before sorting. And make sure it sorted correctly before you re-save. That is, that the other items in the row sorted along and stayed with their appropriate item in the first column....
One more sorting note:
I think this works in Excel...
<I>Field 1 Field 2 Date________________
Company Item Description #On Hand # to Reorder</I>
I believe with the above fields, you can sort by Field #1, with #2 as your secondary sort field. That makes it easy to reorder. Then when you just want to know what you have, and put all similar items together, you can sort by ONLY Field #2, and ignore Field #1.
Did I miss anything?
Or does anyone else have a method they like better?
I used something pretty similar to this a long time ago, but it was less orderly than what I've now suggested.