How about Dal's "Artigiano" series. Looks like hand made tiles so it adds some interest but not too busy. Here's link: http://products.daltile.com/series.cfm?series=462

Not a huge fan of that tile....

I like the look of herringbone....

http://www.homedepot.com/p/Splashback-Tile-Royal-Herringbone-Sand-Polished-Marble-Floor-and-Wall-Tile-3-in-x-6-in-Tile-Sample-M1C4HDRYLSND/206656095?MERCH=REC--NavPLPHorizontal1_rr--NA--206656095--N

Any suggestions on color & size?

The 3 x 6 usually fits the best imo. Like this one I did in the picture . I like staggered but You can also run it herringbone which is popular choice.

yeah, I'd stay away from the marble herringbone, as I think it would feel too busy with your counters. but a simple subway tile in white (given your white appliances) could be run in herringbone for a little subtle interest.

If you're going to use a plain light tile, I think your walls need a different color paint for some contrast. Something deeper or more vibrant. Otherwise the kitchen is very brown/beige/blah.

Pale salmon subway tile? to pick up the salmon hue in your marble and accent your wood that has reddish tints.

Wow the photos that acm provided look like some great options for your kitchen! Those subway tile designs could really elevate your kitchen from nice to awesome. And they are surprisingly subtle. Good luck!

i think a white subway tile would look awesome either staggered or run herringbone

I am working on the same type of decision. You are right to keep it simple. With movement in the cabinets (because of the grain) and movement in the countertop, the backsplash needs to be simple or there will be too much movement. I am looking at a white or cream subway tile. I will wait till the counters go in to make a final decision. You can get both white and cream subway tile at a home center store, very inexpensive, and put together your own sample boards to see which goes best. I have similar white trim and wall color. (pics in my idea book) I am concerned the white will be too much contrast for me, but not sure about the cream either. Both match my sample countertop. Since my countertops are not in yet I am still deciding. I may do something with a little bit of color over the stove.

I am thinking of something like this:

I would suggest the Crema Marfil mini brick tile.