Need a super cheap DIY bookshelf that won't take up too much wall space? Check out this instructable tutorial for making "invisible" bookshelves! All you need for each shelf is an old hardcover book (that you don't mind destroying), an L bracket, some screws, glue, and basic tools.

I made those 2 awhile back in my old apartment - I think they look really cool spaced like that, diagonally on the wall with smallish book stacks. In my current living space, however, with my book-buying habits, and living here in Portland (the bookiest city I know), I have a crazier shelving system:

That's just 3 of the shelves, with pretty massive stacks on each one. They hold up well, and are super easy to put up. They'd be great for college dorm/apt living, if you can put in a few screws - you just need one screw in the wall per bookshelf. Of course, these can only hold your smaller paperbacks, the big books need to live somewhere else. The best thing about these shelves is definitely the reactions you'll get from friends! So confused!