Found this list online the other day in the LA Times:
88 Books that Shaped America
I've read 22 of them (and yes, that includes The Cat in the Hat). And I continually refer to one of them (The Joy of Cooking -- though I have a much more recent edition than the one listed).
I actually like this list. I think you could probably come up with more books that belong on it, but it's a really nice mix of fiction and nonfiction, writing for all ages, writing by both black and white authors, time periods, etc. There's even a little genre fiction on there (Stranger in a Strange Land).
The list was compiled by the Library of Congress. You can read more about it here. (There's even a survey, if you're so inclined.)
It gives me some good ideas, by the way, for my out-of-genre project. I used to enjoy a good hardboiled detective novel, and seeing Red Harvest on the list reminds me that I have a couple of Dashiell Hammett and Raymond Chandler books on the shelf. That would be a little different from the stuff I usually choose for those posts.