What are some awesome lift-the-flap books (for kids and grownups)?

I read all these suggestions waiting to see Where's Spot, and finally telepanda got to it. It is the BEST for very young children. A hide and seek game while sitting in your lap. Another book my kids liked is http://www.amazon.com/s/ref=nb_sb_ss_c_0_16?url=search-alias%3Dstripbooks&field-keywords=monster+at+the+end+of+this+book&sprefix=monster+at+the+e%2Caps%2C380 It does not have flaps, but it has suspense on each page so that just turning the pages is the activity which inspires squeals of delight. Grover is constantly warning your child "Do not turn the page, PLEASE!!!" and then "Oh, No, you turned the page!!"

The http://en.wikipedia.org/wiki/Ologies_%28series%29 books? They are definitely for older kids, and have lots of non-flap materials as well (small mini-books, "artifacts", etc). Maybe more for you than your kids at this point, but they are ridiculously popular with older elementary students at my library - they circ so much and have so many little bits, I have to replace them once every 2 years or so. Your 4 year old might like them in small doses, and they'll certainly enjoy them more when they're older.

I had an incredible one about the life of Leonardo Da Vinci when I was a kid. It had http://www.brainpickings.org/2014/06/18/leonardo-da-vinci-provensen-pop-up-book/ in it, like flapping the wings of a flying machine, making the stars circle overhead, etc. http://www.amazon.com/exec/obidos/ASIN/0091591104/metafilter-20/ref=nosim/. Unfortunately it's out of print and used copies are $177.

On the adult tip, you should check out "http://www.amazon.com/exec/obidos/ASIN/B00NDTS5E8/metafilter-20/ref=nosim/" by Murakami, "http://www.amazon.com/exec/obidos/ASIN/0316201642/metafilter-20/ref=nosim/" by JJ Abrams, and especially all of the books in the http://www.amazon.com/exec/obidos/ASIN/0877017883/metafilter-20/ref=nosim/ by Nick Bantock.

Seconding Karen Katz. Our 20-month old loves http://www.amazon.com/exec/obidos/ASIN/0689835604/metafilter-20/ref=nosim/ and http://www.amazon.com/exec/obidos/ASIN/0689847122/metafilter-20/ref=nosim/.

http://www.amazon.com/exec/obidos/ASIN/0316126446/metafilter-20/ref=nosim/ by Allan & Janet Ahlberg is delightful. It has lots of teeny letters from fairy tale characters that you can take out and read.

Check out the works of Robert Sabuda - get hands-on if you can. They're primarily pop-up books, but incredibly intricate and beautiful. Some of the books have interactive elements as well. Definitely on the more fragile end, but kids (and adults!) love them.

http://www.amazon.com/exec/obidos/ASIN/0689825730/metafilter-20/ref=nosim/ is amazing in its attention to detail.

Ok this is more of a pop-up book BUT the pop-ups have flaps and strips and whatnot and it is pretty great: https://www.youtube.com/watch?v=wnZr0wiG1Hg.