Here are some ideas: a definite must is the old world style of Winnie the Pooh’s original illustrations and Alice in Wonderland, and Through the Looking glass.
A great picture book is the wordless, but very moving The Angel and the Soldier Boy. Besides Spot the dog, there are the great little picture books of Clifford the Big Red Dog, and Jillian Jiggs [a girl with a hilariously messy room and great illlustrations], the sweet little mouse Frederick the poet, the big, adorable, neat picture book The Golden Egg and the little picture book about Little Black Sambo, who outsmarts tigers and has pancakes with his mom and dad [he's from India in my version/copy of the book].
Also try the illustrated 'choose your adventure-style' picture book The Maze, which you can even ‘read’ online. It’s an actual maze, each page is a door. The pictures are really incredible, and it just draws you in. It's a great early book to get you ready to look at art in museums and notice details, so that you can enjoy the work even more. And most of all, it's crazy fun!
Masquerade was another puzzle type picture book that sucked me in. It’s very difficult to solve. It has neat art.
This illustrated, large picture book of the Wizard of Oz with the best illustrations ever done by Charles Santore is a great one. Also look into the great fairy tales with medieval-like illustrations like Beauty and the Beast & Sleeping Beauty & St. George and the Dragon.
Sendak’s Where the Wild Things Are was amazing classic with great art, as was sad, more serious chapter book The Secret of the Andes, a book that still makes me nervous [it is similar in tone and style to the very terrifying and tragic story of The Island of the Blue Dolphin.
For the A-Z alphabet learning, try Animalia by Gaeme Base, it has such gorgeous images that it should still be bought simply as a coffee table book. It's really amazing and detailed, like Bosch level thought was involved.
Mercer Mayer’s little critter books were so cute and sweet, My Cousin Katie is on a farm for old fashioned memories, Arthur the aardvark for fun stories. Also look into the excellent, incomparable and top illustrated books [and later cartoon tv show] of The Busy World of Richard Scarry [with the fun, Austrian dressed character 'Lowly the talking/walking [on one foot!] worm' and his flying apple car] and the famous, lovely book about Maine, Blueberries for Sal.
I also loved The Water Babies gorgeous, real art picture book, where a young boy goes to a magical land of sea creatures; the illustrations are amazing.
Halloween themed books were great too, like Nightmares: Poems to Trouble Your Sleep. Little Witch’s Big Night by Deborah Hautzig was great–the illustrations were so adorable. The best book of all was a book of interesting scary stories called Now you see them now you don’t–it has fascinating, subtle stories that are more strange and ghostly than horror.
As a kid my only cookbook was a cookie one, the Alpha-Bakery Gold Medal Children’s Cookbook. Each letter has a recipe and it has very cute illustrations. I still love it.
For young people: From the Mixed-Up Files of Mrs. Basil E. Frankweiler. What an introduction to the Renaissance, museums, the ancient world, sculpting, art and life, I loved it once I realized where it was going--and even then it always surprised me. Also look into Redwall for mystery and adventure lovers, Nancy Drew, and The Egypt Game [which for lovers of history, art, mystery and Egypt is more loved than the more famous The Westing Game].