Don't know what stores you have around you, but a lot depends on the weight of your shelves and whether or not you want floating shelves or shelves with brackets. A lot of the floating shelves are built for decorations/pictures/etc, not books. A couple of options for you, though...Pottery Barn has some
floating shelves. Their 2' shelf hold like 35lbs, their 3' shelf holds like 55 and their 4' shelf holds like 75lbs. (weights were told to me by a sales rep at the store)
Also, Ikea has a shelf that has two wrap-around brackets that hold a custom-length shelf between them...might be a good idea for you. (I think
THIS is it)