I'm pretty discriminate with my children's books. I've discovered there are some real duds out there. When You Were Small is my favorite of late, it has just the right amount of whimsy paired with show-stopping illustrations. I finally got my son to love it and I take it as a personal victory. It's way beyond rad.
In another life I worked at a tiny independent book store in San Diego and amassed some of my favorite art books. I spent the better part of my wages on these titles. Of course I've learned a good book can be found most anywhere. I especially love these Family Of Woman, Family Of Man photography books from the seventies, they contain some heart stopping images. Keep your eye out for them at thrift stores and estate sales for pennies on the dollar.
Check out these cheesy titles I stumbled across at the Savers in Redwood City (which is so massive, it takes up a whole city block). Looking (and not buying them) just made me happy.