I found some pretty scenes at casual-effects.com/data/. To render them I had to overhaul my materials and write an MTL parser to go with my OBJ parser. I also implemented support for bump maps, texture maps (both require handling the 'vt' lines in OBJ files), and learned about height maps vs. normal maps vs. displacement maps so I could write a script to turn greyscale height maps into RGB normal maps.
On this Sibenik Cathedral image, check out the relief near the bottom, left, and right sides of the image. The normal maps really pay off when the surface is in partial shadow.
In this Cornell box the water sure looks great! This entire box is rendered from an OBJ file with the materials described in a corresponding MTL file. (I'm also working on implementing photon mapping so you can see some color bleeding from the red and blue walls.)