I was browsing in a second-hand bookshop yesterday and I came across a Bulgarian/Esperanto dictionary, marked down to $1. What a bargain!
Two actual books currently in the $1 book section of a local BOOKS A MILLION (retired public library books still in mylar):
The Three Little Pigs Go to the MAll of the Americas (a children’s book)
and
*Know Your Ocelots and Margays *
I’d buy the second, if only for the photographs. (There ARE photographs, right?)
Cinder the Cat, a children’s book from 1931. This seems very early considering the non-superstitious, cute-kitty treatment of the title (black!) cat.
I know someone who speaks both those languages. Wanna send it to me? I’ll pay postage and packing. 
Not esoteric, but in a thrift store, I immediately grabbed up How To Talk Dirty and Influence People.
Loved it. I think it was 20 cents.
I recently saw these titles in my local used book store:
"If You Leave Me, Can I Come, Too?
“If You Can’t Live Without Me, Why Are You Still Alive?”
“Get Your Tongue Out Of My Mouth; I’m Trying To Kiss You Goodbye!”
I can almost hear the twang of pedal steel guitars in the background…
I used to work in a bookstore, and the good-natured staff would keep notes on utterly ridiculous titles that we’d run across from time to time. Sort of a running contest, “Top THIS book!” Anyway, these are a few that I remember:
My first day in the “help desk”, a gentleman asked me if we had any books on ornamental onions. “HAHAHAHA um let me check,” and as it turned out, we DID have a coffee table book on Alliums. Whenever odd books were being showcased, the $49.99 hardcover copy of Alliums was usually trotted out.
The “Everything Tastes Better with Bacon Cookbook” was also a longtime entry - included such classics as the recipe for Peanut Butter & Bacon sandwich (Now, I’m not saying there’s anything wrong with PB&Bacon, but if I wanted one, would I REALLY need a recipe??) and also a section on Bacon DESSERTS. Apple & Bacon crumble actually sounded pretty darn good. It was damn strange though.
The title of this art coffee table book escapes me, but the topic was circus porn. It was kept behind the counter, encased in cellophane, but you know us nosy booksellers cracked it open for a look anyway. Bridget the Midget was featured in all her glory on several pages.
“The Chick is in the Mail” a compendium of short stories (fantasy, medieval settings) featuring women in the lead heroic roles. A couple of the stories were quite good, we just loved the title. Alas, it didn’t sell well and was stripped and sent back to the manufacturer after a few months.
Aquarotica - a compendium of short erotic fiction pieces, all featuring water. The best part about this book? A symbol in the upper right hand corner, denoting “This book is waterproof.”