So, Casascius's new product is an aluminum bitcoin with no backing-you're supposed to make your own. If it was me, I would use bitaddress.org, generate a barcode for the public address and private key. I'd print on mailing labels or something. I would put the QR code of the private key on the back of the coin. I would set up a document explaining in greater detail what the coin is, how to redeem it, its public address, etc. I'd host it on any number of file sharing sites. I would then make a QR code of the link to that file. I would print it out and stick it where there is a designated spot on the card below. This way seems like the most efficient/effective way to use these coins.
However, it would be awfully confusing to someone if they just scanned the QR code on the back of the coin-they'd get a number of digits and have no idea what to do. Thats where the card I mentioned comes in. I have some professional business cards of the design below. They work perfectly to leave with one of these new Casascius coins (say...as a tip at a restaurant). The back of the card is just going to be a background of the image (you probably know it) like is on Casascius's site. I'm going to add a small "Vires In Numeris" in white font on the bottom center of the card. I'll get a picture up asap.
If you ordered some of these coins, I think you really need something like this. I'm not going to put a price because I always prefer agreeing to one on a case by case basis. However, I can assure you that the price for these will be peanuts (if you don't know the expression it means "very cheap"). I'll ship any quantity anywhere in the world. So, if you are interested, please just shoot me a PM!
The picture below is what the actual card looks like. It is designed to be the size of a standard business card (2''x3.5''), and so it may appear a little distorted-I just wanted to make it big enough to see clearly.
