I love the look of what's usually called a chunky shelf, but the prices charged for most of them border on the criminal. Here's a cheap do-it-yourself project I found on Reader's Digest's website of all places. All you need is some basic tools, a couple of hours and an appreciation for cheap fixes that don't look cheap.
1. Pick up an 18" or 24" wide hollow core door or two.
2. Mark the studs on the wall where you want your shelf to go.
3. Using either a table saw or a circular saw (use a fence or some kind of straight edge if you're going the circular saw route), and cut the door in half.
4. Hollow core doors are actually not hollow. They have a corrugated cardboard core. Take a wood chisel (or a steak knife) and remove the corrugated cardboard center.
5. Measure the inside dimension of the thickness of the door. Round the number down to the nearest eighth inch.
6. Cut a 2x4 to the thickness of the inside dimension of the door's hollow core. This 2x4 is the cleat that will hold up your shelf and make it appear to float.
7. Draw a straight line across the studs you've already marked on the wall. This straight line will be the line where you set the bottom of the cleat.
8. Screw or bolt the cleat to the studs through the wall.
9. Apply carpenter's glue to the top of the cleat and the lower inside of the back of the shelf. Slide the shelf onto the cleat.
10. Fasten the shelf to the cleat with 1" brad nails space 8" apart.
11. Allow the glue to cure and paint your heart out. Paint them any color but the blue in these photos, please.