These had the exact proportions I was looking for at a reasonable price - you won't find 5' floating shelves for any cheaper, unless you are handy and can make your own (which I can't).  

I found these relatively easy to install on my own.  They are pretty lightweight.  However, the directions aren't the easiest to decipher - they don't include as many screws as there are holes in the bracket, and the illustrations in the directions don't exactly match what the pieces look like.  

My other issue is that these do tend to sag after a few weeks.  I'm likely going to have to install small support brackets around mine (a pain, since the whole point of a floating shelf is to avoid that look in the first place).  I haven't even put anything that heavy on mine - just a few small bottles/votives and a basket of toilet paper.