I've seen them at the Container Store.

Here is a link that might be useful: Container store floating shelves

Lowe's has some, but I've never looked at them close-up to see how they're made or how they're attached to the wall. (Ikea's have those heavy metal pieces with rods that stick out and into the ends and middle of the shelf.

I would not put books on the IKEA shelves. I have pottery on some IKEA shelves and they seem to be holding up well -- but they also don't get the contact, on-and-off action that a bookshelf would get. But this photo will give you an idea of whether they (or other shelves of their thickness) look substantial enough for your needs.

I don't know that there are many floating shelves that "off the rack" can support the weight of books. You may have to look at getting something custom-made. I saw some interesting metal shelves once in dwell. Very thin steel metal was fabricated in an "L" shape with one leg of the "L" fastened directly to the studs of the wall, and the other leg sticking out horizontally to form the shelf. Then the drywall was applied BETWEEN the shelves. You could then attach a chunky shelf to it. But that would entail tearing your house apart!

Barring that, I'm not sure how to do it. There are these from PB that have up to a 100# weight limit. (I think IKEA's are only something like 15-25#).

Here is a link that might be useful: PB floating shelves

Target has a nice selection of floating shelves.

My son has the LACK shelves in his room.
They held books, a boombox and a huge assortment of things that a teenager collects.
They are very substantial!

I think most any shelf (and the load it carries) is as good as HOW it's attached to the wall....

I have the shelves from Pottery Barn and they hold all of my everyday dishes , so the weight is considerable. They have been perfect for 4 1/2 yrs so I think that is a good test. We take the plates etc on and off daily. Here is a pic...they are quite thick also so look substantial:

I find the floating shelves with long brackets can hold a lot of weight. I've seen the ones in the link below at my local hardware store. They look great. You just have to make sure to attach the brackets to studs or to drywall with toggle bolts or something similar.

I used similar brackets with cheap 5/8" thick particle board shelves for heavy cookbooks. It worked for years. I only pulled them down because I repurposed that part of the room.

Good luck.
Lisa

Here is a link that might be useful: Floating Shelves

I bought the one from Lowes and it has long rods to add support for the shelf. If you screw it into studs you'll have no problem with books.