Like amy, we just let our glass mosaic tile "end" in the previous house's kitchen backsplash and the current house's master bath wall tile. The edge is caulked, but is slightly rough when you run your finder over it. I have a long horizontal edge behind the vanity sinks (about 7" above the sinks) and I have not found it difficult to keep clean or anything. I like the simpleness of just letting the glass tile end. In our installations, any edging would have been too fussy...

We have the same layout and used marble tile. Since you are using real stone, they may be able to bullnose or bevel the edges. We used a pencil liner, but since they came very tall (thick), DH cut them down so they weren't so much different than the tile. You would not be able to do that very well with ceramic, but it wasn't a problem with the stone. Here's ours, so you can see what it looks like with the pencil edging. I really didn't want to use the liner pieces, but left it up to DH to decide how he wanted to deal with it.

I have a white/gray stone tile and it's thicker than a typical subway tile. Tonight at Home Depot I put a Schluter brushed metal tile edge against it and was surprisingly pleased with the result. Even though it's a vintage (1920's) style kitchen, it works with some of the modern elements like the stainless steel fridge and lighting fixture.

ajracine, after I thought about your question, are you saying to take the 2"x4" inch (that is on a 45 degree with the herringbone) but run them in a straight pattern along the edge to line it? That would work. You might sacrifice a sheet to see how it will look to you. As long as you are okay with a 2" wide line of tile running vertical. Those would not need to be "polished off/bull nosed" like I was talking about. In my earlier reply, I was envisioning "rounding off" the cut edge of your mosiac. Sorry about that. I think I now understand. I think I would still go with a shluter edge or a thin pencil liner tile (if it blended well with your mosaic herringbone.) The reason I say that is the border you would created with the 2x4 tiles will pull your eye to the trim line/herringbone joint line, and take away from your pretty herringbone pattern. (or that is what my mind is seeing.)