Good art can be hard to find. A lot of the stuff in stores is just not great and there is some decent art on Etsy but that can be pricey. I came across this website, Vintage Printable, which houses thousands (millions?) of copyright free images. These are usually older images scanned in at a high resolution and says right on the website they are "images in the public domain believed to be free to use without restriction in the US." Find some images you like, make sure they are high resolution (good clarity for printing) and print either at home, in a store (CVS, Walgreens, Costco) or order online (Snapfish, Shutterfly).
Use the links at the bottom of each category page, then right click to open your image in a new tab. Click on the image and zoom in, then right click to save to your computer. This will ensure you have the highest resolution (largest size). Before printing, I like to open in PicMonkey to make sure the size & shape is what I want.
Here are some of my favorites:
Black background botanical prints
here and here
There are a lot of animal images to choose from, I like these bears:
here and here
Get a little weird with a portrait of a random woman
1. woman green mountains
2. woman in gray
3. florence, headcrown
4. girl with flowers
Illustration: Palace women hunting here
Eiffel Tower circa 1910 here
Let me know your favorite images!
**Update: I just came across this site and had to share as well: Shorpy Historical Photo Archives
Can search by location or subject and the images are AMAZING resolution. Check it out. Love the Detroit ones.