J.M.
I have a TON on Facebook... Not technically a photo storage site, but it works for me! lol. Plus, they are in a place where they can be enjoyed by everyone instead of just sitting on some website... lonely... unviewed... (lol.)
Other than that, I back up all of my pics on an external hard drive. I lost several years worth of pictures when my old computer crashed, and I don't want to take that risk again!