...I was wondering if LARGE paperbacks have a name designation. For instance, Stephen King released his Gunslinger series in a collectable-type paperback, and the books were about the dimensions of a standard hardcover book. So, monster-size paperback books.

I traipsed around Google/wikipedia for a while but couldn't find anything referring to this. I think a couple people that I sent those books to might have been a bit shocked that they couldn't just toss them in their purse.

I always thought they were called Trade Sized paperbacks.

I always look up on Amazon if I can't figure out if a book's a Mass Market Paperback or a TS one.  Some books are published both ways and I prefer a TS if I can get it.

This works in my favor when buying books at the Goodwill Store, because they charge less for paperbacks than hardbacks. There is bound to be a trade name for them. Not  "pocket books" that's for sure.

These were much larger than standard trade size that I usually see. 

But I don't think that there is a standard for the size of trade paperbacks.    Trade size just means that it's not the standardized mass market paperback size.   I agree that most of them seem to be around the same size, but there are also some that are really large and some that are even smaller than mass markets.

So these would be trade paperbacks.   

Mass market used to be used to describe the smaller paperbacks often sold at grocery stores and drugstores. Trade paperbacks were traditionally larger (often the same size as a hardcover), used better quality paper, and were usually only sold at bookstores. The line between them is a little blurred now with discount stores selling all types of books and the introduction of the taller mass market paperbacks. Personally, I don't like the taller MMPs because they don't open easily and no matter how careful I am I tend to crack the spine. Plus they don't fit on my bookshelves with MMPs and get lost with the trade paperbacks.

I like to sandwich my paperback books between two pieces of cardboard before mailing them, so I have a stack of cardboard rectangles next to my mailing supplies. The two sizes I use the most, other than standard MMPB (about 7 x 4 1/3) are the 6 x 9 and the 5 1/2 x 8 1/4. Perhaps one of these is the standard "trade paperback" size?

I have all sorts of odd sizes of paperback books, though. Just grabbing a couple off my shelf, I have one that is 11 1/2 x 9 and one that measures 6 x 4. I just cut the cardboard for them after they are requested.

Yuppers, the big ones are tradesize and there doesn't seem to be one standard size for those.  The regular MMP is what used to be referred to as a pocket book.  Then there's that new size, basically MMP but a bit taller...those have a special name but escapes me just now.  They were supposed to be easier to hold and read, but many readers don't seem to like the size.

You may be thinking of a "tall paper back", where a paperback with the same dimensions as the hard cover is released at the same time as the hardcover.  This is not a commonly used term, however.  In any bookstore, these are called trade paperbacks, and they can vary in size from teeny-tiny gift books to huge coffee table sized books.  Any paperback that isn't a mass market or pamphlet/chaplet is a trade paper.

Thanks for the answers.

I've been calling them "expensive phone-books" up till now. 

The general term would be "trade paperback".

There are more precise terms for a variety of exact sizes (folio, quarto, octavo, etc.) , see http://en.wikipedia.org/wiki/Book_size as a starting point.