I wish I had my old Dr. Seuss books now, but alas, they went the way of most abandoned childhood things. So, I'm thinking of re-acquiring some. Here are some first editions. They're pricey now, so if you collect, seek out some slightly later editions. That's what I do with most books I collect, often going with later editions or later printings of firsts. Lots of early editions can be found on eBay. Heritage Auctions has some interesting editions, some signed by the author.
"New socks. Two socks. Whose socks? Sue's socks." Fox in Socks. Beginner Books, A Division of Random House, 1965. First edition.
"I’ll load up five boats with a family of Joats / Whose feet are like cows, but wear squirrelskin coats, / And sit like dogs, but have voices like goats— / Excepting they can’t sing the very high notes." If I Ran the Zoo. New York: Random House, [1950]. This one sold for $1314. on Heritage Auctions
Dr. Seuss. The Cat in the Hat. [New York]: Random House, [1957]. First edition. Signed by the author in blue ballpoint via
"In the places I go there are things that I see / That I never could spell if I stopped with the Z. / I'm telling you this 'cause you're one of my friends. / My alphabet starts where your alphabet ends!" Dr. Seuss. On Beyond Zebra. New York: [1955]. First edition, first issue dust jacket. via
“Then the Grinch thought of something he hadn't before! What if Christmas, he thought, doesn't come from a store. What if Christmas...perhaps...means a little bit more!” How the Grinch Stole Christmas. New York: [1957]. First edition, first issue dust jacket. Sold for $437
Here's a really early one that I wasn't familiar with. "And to Think That I Saw It on Mulberry Street" New York: The Vanguard Press, 1937. sold for $1195 on Heritage Auctions