Making a custom play mat

[RoiC.]

After using a laminated black and white A3 grid paper as a map/game mat for a few months now, I've decided it's time to upgrade to mats with backgrounds for each area... Grassland, dungeonfloor, mountains, city... You get the vibe.

Does anyone here has some good backgrounds (preferably gridded, and that will still look good in A3 paper size) that can printed and serve as play mats?

Thanks a lot