Here's another quick and cheap instructable on a floating crate shelf. It cost me $2.77 per shelf! Super easy to do!
Step 1: Grab the Materials
Buy the crate at Walmart for $2.14
Buy the bracket and screws at Lowes for $0.58 and $1.12 respectively.
Step 2: Bend the Bracket
Use vise grips to bend the bracket to form a 45 degree angle.
Step 3: Attach to the Wall
Screw the bracket into the wall.
Check the fit. Adjust the angle with a mallet if necessary. Recheck the fit. Make sure it doesn't sag down and you're done!
Add another if you'd like!
Thanks and enjoy!