For a preschooler:

Especially looking for Usborne books, books about nature (including Little Golden Guides, even though they aren't really for preschoolers, he still likes looking at them), Berenstain Bears books, National Geographic Books for Young Explorers, Backyard Buddies books by Michael Ross, Mr. Men and Little Miss books, I Spy books, Magic School Bus books, Reading Rainbow books, picture books by Joseph Bruchac, anything by Gail Gibbons, Jim Arnosky, Lucy Cousins, Richard Scarry, Todd Parr, Eric Carle, or any other age appropriate quality children's literature. 

For a 9 year old:

Looking for Horrible Histories, Horrible Science, Horrible Geography, Myth-o-mania, Animorphs (#42, 46, 48, 50-53), kids cookbooks, and books about origami.

Also looking for Blue's Clues books (especially interested in board books) and board books by above authors for my toddler.

I know a fair number of these things are wish listed, but I WILL GLADLY ACCEPT UNPOSTABLES IN READABLE CONDITION.  Thanks.