This is a design I came up with a few years ago because I got tired of wasting space with bookshelves and small little media shelves from Wal-Mart.
Normal game/movie cases are 5.25" across, so using a 6" board gives you the perfect depth to have them sit practically flush on the shelf. And with the board being only 1"...which is actually 0.75" (yay lumber standards!
)...as opposed to the 2" suggested above, you've got less space being wasted between shelves. 0.75" may not seem like it would be very strong, but it's thicker than most shelves you'll see in any store.
1x6 boards aren't as common though. They're basically deck boards, so that's where you'd need to look. As for the shelf's height, obviously, you can change it based on your needs. This was basically for a floor to ceiling set up (which you'd probably want to anchor to the wall...also, make sure your ceiling allows clearance for an 8' board...you may have to trim it an inch or two shorter depending on your carpet).
For the width, I've got 6' long boards cut in half, but really, you could just stick with all 8' and cut them into thirds (8' = 96", 96 / 3 = 32) and only lose about 4". I thought 8.75" space between the top of one shelf and the bottom of the next was pretty good since standard dvd/xbox cases are 7.2 inches tall...which gives you a little extra room for any collector's editions an abnormal cases you may have.
That's pretty much it. Before this, I had a crappy $30 bookshelf from Wal-Mart, which held things fine, but it was much deeper than necessary. So, movies were getting stacked in front of and on top of each other, and it was just horrible to try to look through. This shelf only sticks out 6" from the wall, and can hold over 800 games/movies if you go with the 8' design. Much more efficient!
