Sometimes the simplest project is one that you use the most. I love this one because I have a lot of books, most bookmarkers are useless because they fall out so easily, and this bookmarker is cheap. The only tool required is a pair of needle nose pliers and the only material is some flexible wire. I use 16 or 18 gauge enamel coated magnetic wire that I use to make radio coils - but any wire will work that you can bend easily.
The pictures tell it all I guess, just use your imagination and bend some wire. Be sure to coil both ends so that the pointy end doesn't poke your eye out.
I like these kind of bookmarkers because you can squish them tight so that they don't fall out of the book.
If you buy this style of bookmarker, they are usually fairly expensive. Now you can make all you want for almost no cost.