I was looking through websites when I came across a link to this. I was like "Wow, I want one of those! In fact, I could make one!" So here it is!

Step 1: What You Will Need....

So for this you'll need:
A wooden dowel (I found one in my mom's closet full o tools and things)
Duct tape (Very easy stuff to find)
Surveyors tape but preferably something stronger. (Mine was $2. You can get it at someplace like Ace. It isn't sticky, it's just for things like tieing on stakes to outline something on the ground like where a house will go. You could also use other things instead.)

Step 2: Take the Tape And....

The wooden dowel found was 21 inches long and I used roughly 15 pieces of surveyors tape that were 2 feet long. You can use more or less and make the pieces longer or shorter.
So cut all the peices of surveyors tape you need and then tear off a piece of duct tape as long a your dowel. Put it on one end and take a piece of surveyors tape and loop it over the dowel and tape it down. Keep doing this until you have put as many loops on it as you want it to have. Put them close together without too much of a gap between them.

Step 3: Smashed Mutant Octopus

So by now your bookshelf should look like a smashed mutant octopus. The loops might not exactly stay on very well so take a piece of duct tape and rip it in half and stick it down on the underside of everything. Put the tape on the bottom by putting the loops around the ends of the dowel so that you don't accidently tape the surveyors tape to the dowel.
If you find that it still doesn't look like it will stay on put some very thin pieces of tape between each of the loops to hold everything on a little bit better.

Step 4: Almost Done!!

Yay! So you're almost done, but if you try to put a book in your book "shelf" it will just turn to the side and fall out. Soo take some pieces of surveyors tape and tie them to the very top of the loops. Now the book should stay in.

Step 5: Bam!

You're done. This project cost me less than $5 but might cost more dependion on how big you want ti and stuff like that.
Enjoy your smashed mutant octopus bookshelf! If you have any questions just ask :D

Step 6: Individual Book Holder

Kiteman told me about [http://www.core77.com/bullitts/2005/08/House-Special-Solo-Bookshelf.asp?current_bullitt_number=0¤t_bullitt_id=296 this] one. It holds only one book but it's really easy to make.
So take what ever you're using, (surveyors tape, caution tape, cloth, etc.) and if it might rip because of the thumbtacks/nails you should put duct tape on the end. Put the ends together and put a thumbtack (I wouln't suggest thumbtacks) through the ends and hang it on the wall. There you have it! Put books in it just like you would the other one.