Earlier in my programming days, my go-to example would have been foo.com. Well, not always. If we had any inside jokes on the team, I might put something clever in there for fun. On the Cloud Foundry backend team, one of our current inside jokes includes a picture of Bob Ross in the free space on one of our CI boards, so maybe in that case I would have gone with bobross.com or paintingclouds.com, just for fun, if I needed a fake URL for a test.
I think it was Ken Mayer who taught me that example.com is actually meant to be used in documentation and tests. example.com isn’t just some domain that some private party is using for the greater good; The Internet Engineering Task Force published RFC2606 which specifically says that example.