We have found some awesome new books lately! It seems that more publishers are realizing that homeschooling is growing substantially and they're accommodating by coming out with some great materials.
Smithsonian has these Super Simple books and I got all 3. They are laid out very well and of course super simple. I find that these can work in any grade, though they are advertised as for grades 6-12. Adults will even find these valuable!
Z really loves these Ultimate pop-up books, he has looked through them countless times since getting them a few months ago: