Mine is made of items destined for a landfill: a halogen lamp and wire hangers.
If you have $40 handy, stop reading right now and go buy a "CD Seller" from Jeff Kartak: http://www.thecdseller.com
Jeff seems like a good guy who has made a solid product with a proven track record out of quality materials, and if you can manage it, do give him your business! It's thick plexiglas and mounts to a mic stand.
I've been doodelling ideas along these lines for years, and was making due with a simple wire CD holder made from a clothes hanger: it worked (and was actually kind of cool), but it required me to ask somebody to help me, or wait until between songs, to sell a CD. Sales are lost because of little obstacles like those. But as Jeff has figured out, a self-service display solves the problem (I'll spare you all of the arguments for and against, because you can read them at CDseller.com).
Step 1: Materials: Landfill Fodder
-Old "Torchiere" style Halogen floor lamp
These are power-guzzling fire hazards that are vanishing in droves. You either already have a broken one in your garage, or your friend does. The one I had was white, black would be better.
-Wire hangers or Welding Rod
Hangers are versatile, reasonably strong, and plentiful. If you've managed to convert completely to plastic or wood hangers at your house and don't have the plain wire kind, go ask a dry cleaner: they're eager to offload. On a side note: don't eat these, and you might want to wash your hands after playing with them: they're made of low-quality metals and you just never know what exotic ingredients might be included in their composition. Welding rod isn't usually as free as a hanger, but will give you a nice, brass look.
I used a piece of pine, cut into an 11" x 4.5" rectangle.
The kind used for canning, with a two-part lid.
-Large bolt, washer
With threads that match those in the lamp's poles. May not be needed, depending on how your lamp is put together.
Optional. I used black "no-skid" spray paint.
-Hot glue gun
-Optional: Spackle or drywall putty, Rasps, files, sandpaper
Step 2: Drill & Cut
Drill a hole in the geographic center of the board- the final size depends on the lamp hardware (see step 5).
Trace a circle to the right of the hole you drilled, using the threaded "ring" part of the lid of the Mason Jar.
Your circle's edge should be about half an inch from the sides of the board.
Cut out the circle you just traced, by drilling a pilot hole, then following around with your jigsaw blade.
Optional: Round off the corners of your board, leaving a half inch of wood around your circle.
Clean up your cuts using files and/or sandpaper.
Step 3: Fit the Lid
Sink the lid ring that you traced into the hole you cut (make sure its "lip" is facing down and its top is facing up)
File or re-saw as needed for a good fit: you want it to be level and flush with the top surface of the board.
Glue it into place. Fill gaps with drywall putty or spackle, or just use lots of hot glue.
Step 4: Disassemble Your Floor Lamp
These lamps usually come disassembled when new, so it should be no trouble to take it apart.
Remove the whole lamp assembly and the top tube (there are usually three tubes). This should all just unscrew.
You won't be needing the power cord or the switch, so you can remove them: the power cord is usually threaded in from below, and knotted inside the lamp's base. Cut the power cord and pull it out. You may need to cut in more than one place, remove a screw or two, but you'll easily win this battle.
Save the bolts and screws, you may be able to use them later for mounting, possibly eliminating the need for any additional bolts.
When you're done with this step, you'll have a stand about four feet high.
Step 5: Mount Your Board
This step will vary depending on the construction of your lamp, but the basic goal is to get your piece of wood screwed onto the stand without leaving a bump on top of the wood.
You may need to widen the drill holes to allow a bolt head to counter-sink, you may be able to use other bits from the lamp, you may need to hunt down the right bolt. But when you're done, your board should have a smooth top surface, and a threaded bolt sticking out of its bottom surface, which will easily screw into the stand with a spin.
I was able to find a nut that fit the threads of the lamp perfectly so all I did was glue a nut into a hole drilled halfway through the board.
Glue the screw into place (not the threads if you want to be able to disassemble), and fill all gaps with spackle or glue.
Step 6: Bend Your Bits
Bend your wire in any way you like: you can make loopy shapes like I did, or use all half-circles, or make squared-off shapes, you can go symmetrical or asymmetrical. I find loopy shapes are more forgiving, but if you start with welding rod or you've straightened your hanger really well, you can get away with a nice machined look.
Other ideas: use old CDs or the clear CD-shape plastic discs that come in CD spindles: sink them into slots in your wood and you can have four "walls" that will hold up your boxed CDs. You'd want to use a clear one for the front, or maybe one wire there and the other walls could be CDs?
Use a few CDs as spacers to help measure where your wire should be mounted.
You want to support the CDs on all four sides, leave just enough space to allow them to be easily added and removed. Drill holes halfway through the wood just large enough to accept the wire. Plug it all in, and check for fit.
A slight tilt in the back and front wires will ensure that the CD's cover is always easily visible, but the side wires should be vertical.
When you like the fit and the look, glue the wires into place. I made little "U" shapes out of ~3/4" wire, and glued them into drilled holes: they act like staples an hold the "CD braces" in.
My rack holds four or five CDs, but you could squeeze on up to ten on a rack this size.
Step 7: Paint
I painted to cover up my shoddy workmanship, but if you've done a nice job it might look great with a clear coat or no finish at all.
Brass or copper-looking welding rod looks very nice with wood grain (just ask Jules Verne).
Depending on what kind of finish your lamp started with, you may want to paint your stand. Mine is an unpleasant beige... no, too light for beige. What do they call that color? Eggshell? Anyway, mine is a definite candidate for a paint job. but look at all the groovy colors the deadly firehazard mothkilling power-hungry lamps come in!
Step 8: Load It Up, Watch It Work!
Load up your CDs, thread your Mason jar into its hole, add a little price tag and you're good to go!
Always a good idea to throw in some seed money, you'll get the added benefit of this serving as a tip jar.
Place your CDs in a good spot where everybody can see it, and watch the CDs sell themselves!
Security: Again, see Jeff's site for this discussion: it's more than worth the very slight chance of the loss of a few CDs here and there, to get the no-labor added sales. And if you pick the right location to set it up, nobody will attempt weasel behavior.
I like how it's asymmetrical but it balances visually as well as literally...
At the moment, this is a bit clunky to carry. It's easiest to carry it pre-assembled, but it's a little tall for some vehicles. You can remove the jar and/or remove the stand, but it's still a bit awkward. So for future improvements, I'd like to see a quick-release instead of threads, maybe a more robust and self-contained (like Jeff's) to allow for easier transport.
I'm also selling a DVD-shaped thing at my shows, so I added a dangling "DVD rack" made of more wire, that just hangs off to the side (more on that later)...
Best of luck, folks!