I am frequently asked what I actually do with my zentangle tiles when I am finished and to that I reply, it's a two part answer.
First: you don't have to do ANYTHING. Zentangle is more about the process than the finished product. If you enjoy it, if you found it relaxing, then zentangle has already done its thing.
But if, as frequently happens, you are happy with the results of your journey, you may want to display them. A friend told me about these boxes at Michaels so I trotted right off to buy one. It measures 2 1/2" by 2 1/2' inches so with the black frame, it's perfect for my colored twinchies. It's made of plastic so if your looking for something really classy, this isn't it, but it suits my purposes well.
My hand colored tiles are done with professional grade watercolors so that's how I get the rich background colors. I tangle them with colored pens and shade and highlight with colored pencils. And yes, I do sell my colored tiles. Click over to the 'store' tab for details.