I find most SD card holders available on the market unnecessarily large and bulky. Hershey's LiquidIce are tiny balls of liquid mint that come packaged in small hard clear plastic dispensers. The dispensers are just the right size for SD card storage. Each can hold up to three SD cards (depends on card thickness. to avoid damaging the cards, DO NOT FORCE fit more than can loosely fit in the dispensers). I am sure it will also hold XD, microSD, miniSD and other cards equal or smaller in size than standard SD. I have thrown away the cases that ship with cards, and now use these LiquidIce cases exclusive.
Step 1: Get LiquidIce
I got mine from closeout at a discount store. You should be able to get these anywhere though. I think they are about 2 bucks for a twin pack.
Step 2: Consume the Mints
Aaaah ... it is finally empty.
Step 3: Remove Labels
You might want to keep your labels, I don't. So I get rid of them. They peel off quite easily, leaving no trace behind.
Step 4: Fix the Cap
The cap has an extra little bit of plastic on the inside that won't allow a standard SD card to be stored in the case. First I thought I might have to cut it out, but that turned out to not be necessary. It simply wedged out with the help of a fork or something similar. On the other hand if you are storing smaller cards, like miniSD or XD, then you may be able to skip this step.
Step 5: All Done!
Now simply insert the SD cards, and snap the cap into place. Like I said earlier, do not attempt to force more cards than will loosely fit in the case. You should be able to get two cards in easily. I have managed to get as many as three in there, but they were all thin versions. You can also stack and bundle multiple containers for even greater carrying capacity!