At compare-calling-cards.com, we take prepaid phone cards from 6 different retailers and compare the calling charges, connection fees and maintenance fees across all of them.
You can compare the calling cards available to dial any destination. Prices given are for calls made from within the continental US. You can also filter out the cards with maintenance fees and service fees.

Each country's page features a comparison table with all the calling cards that can be used for making calls to that destination from the USA. The table has a number of different fields indicating the charges, fees and other terms so that you can choose the cheapest and most appropriate option for your needs.
Calling Card Name: A brand name give to that specific card, doesn't mean much but this is the easiest way to remember your favourite product.
Rate: This is the basic charge in US cents that is deducted from your calling card when you make calls to that destination. It is always a per minute rate, despite the issue of rounding that is discussed below.
Maintenance Fee: The most common type of fee that applies. These are weekly, bi-weekly or monthly charges that are also deducted from the card balance. A high maintenance fee will often mean lower per minute rates, which can be worthwhile if you expect to make a lot of calls in a short period of time.
Connection Fee: Sometimes given other names by the merchant, this is a per call, but is much less common.
Service Fee: Also called taxes by some merchants. Not really the correct term. This is a percentage fee that applies after the end of a call, so unless you are about to use up all the prepaid credit, you should regard this as applying to the per minute rate when choosing between cards.
Rechargeable: If "yes", this means you can add extra credit without needing to get a new pin number.
Rounding: These are the units that are actually used when calculating the cost for international calling. If it's "1 minute" then a 2 minute 5 second call costs the same as a 2 minute 45 second call. If it's "3 minutes"then a 9 minute 20 second call will cost the same as a 11 minute 50 second call. The lower the rounding, the better for you.