Amazon offers its Prime members the CardNinja Ultra-Slim Self Adhesive Credit Card Wallet for Smartphones in Black for $6.95 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping costs $6.03.) That's $1 under our mention from last October and the lowest price we've seen. (It's also the best deal now by a buck.) It's compatible with a range of iPhones and Android smartphones and holds up to eight cards and cash.