Here's a picture of discs that are for component stereo burners, and not necessarily for computer CDR drives. These discs cost more, and are for the most part less compatible. Do not get these unless you KNOW that the person on the other end has a component burner, and NOT a CDR drive. You're wasting money that could otherwise pay for your postage, and might even be wasting your time if the person can't manage to burn them.
Here's a shot of the TDK audio only discs. I've seen these at Sams, and they're expensive. Roughly 3 times the price of buying discs in spindles at Sams. You're really not helping anyone when you get these discs and send them to someone with a normal CDR drive. I know you're GETTING audio on the discs, but audio isn't actually different from data, and it's just a marketing gimmick and a way to add a tax to the discs in the expectation that you'll use them to pirate authentic copyrighted works and the RIAA can profit from the supposed piracy, rather than "lose" money. Evil stuff, so don't buy these.
These seem to be the popular audio-only discs in the UK and Europe. Same deal, they're not necessary. You can get data CDR's for at least 1/3 the price and they work great.