For years I've been using two card holders from Real Simple to organize my loyalty/membership cards. I got these at Target years ago.
Above is a pic of the only still living one- you can see it has definitely seen better days. My red one bit the dust last week. I checked Target and they don't seem to carry them anymore. So I turned to the place I turn when I need basically anything..... Amazon!
I found the kilofly Credit Card Holder on Amazon for just $10 and decided to order it. It arrived yesterday and it is absolutely perfect! This particular style is available in a few other colors, and there are other styles by this brand as well.
Here's a pic showing my cards inside- surely you knew that my Sephora Beauty Insider was one of my most important cards, right? If your purse is a mess of unorganized cards, I'd definitely recommend this!