I have a folder full of business card sheets (twelve per sheet from memory). Each one holds three medium pawns, one large pawn or four small pawns with a medium near the edge to keep them from falling out. I store huge pawns just in a pile. All of them are filed by set and then alphabetically.
I made my solution via woodworking.
I custom-built three drawers, each with built-in dividers, for pawn sizes from left to right: S, S, M, M, M, M, L, L, H. They're arranged by monster type and then alphabetically. I can now flip through them like library card catalogs in old-school libraries.
Sad thing is I have so many pawns I should probably build a couple more drawers, but 3 is all that'll fit in my game cart.
I tried UltraPro nine-card pages, with one large, two medium or four small pawns per pocket. They were unwieldy, and difficult to transport.
Then I bought 3 millimeter foam card (or something like it), cut it apart with a boxcutter, and used it to make storage rows in the original pawn boxes.
Take two pieces of thin cardboard about as long as the narrow side of the box. Height does not really matter.
Glue about pawn-wide pieces of foam card on each in the preferred row configuration. Leave foamcard-wide spaces between these pieces (and at each side; this makes flipping through the contents easier).
Put these backends at the narrow ends of the box. Slot long pieces of foam card (a little lower than a pawn is tall) between the backends.
There is no need to permanently glue this contraption to the box; long strips of foam card are rigid enough to hold the cardboard backends in position.
A pawn box can handle the following configurations.
1. Four rows of large pawns.
2. Six rows of medium pawns
3. Five rows of medium pawns, one row of large pawns.
4. Two rows of small pawns (with two extra rows on top in a detachable tray), three rows of medium pawns, one row of large pawns.
Each row holds about 110 pawns, with some room for flipping through them. Make cardboard dividers as appropriate. Huge pawns are in their own box, but most configurations can handle a few on top of other rows.
I sorted the pawns by type and then alphabetical order, but reserved configuration 4 for summonable creatures, so (almost) everything is easy to find when the conjurers go crazy.
Next step. Where do I store the boxes?
I honestly just use ziploc type bags of different sizes to store my pawns.
For example, I have one large bag labeled "Medium Monsters". Within that bag are smaller bags labelled "Monsters A-C" and "Monsters D-F", etc.
I have seen many beautiful and creative ways of organizing Pawns online, but the advantage of my system is that it is very easy to identify and pull out monsters on the fly. Cleanup is also very quick.
Many of the more beautiful storage systems I have seen online do not seem to be as quick and efficient as my bag system.
If you use a drawer-type system, you have to flip through the pawns and may have trouble seeing the pictures/names of Pawns. Cleanup/ reorganizing is also a bit slow. If you use a folder with plastic sheets, finding Pawns is quick, but cleanup is a bit slow, and adding new Pawns may mess up your organization system (e.g. if alphabetized). With my bag system, you just find the right bag (easy), dump it out (easy), and put the unneeded Pawns back in the bag (easy). Cleanup is equally easy.
I keep my bags in one of those plastic filing boxes with a handle on top.
Pawn boxes. I cut up the cardboard box they are shipped in to use as dividers and keep them all safe and sound.
