What is the best international calling card to use from Western Europe to the U.S.

You can buy any number of pre-paid phone cards from convenience shops over there which will let you call home at low rates.

If you want a good all round permanent card, for calls here in the States and from most other countries to here, I use the IDT global card. http://www.idt.net/personal/cards/gc/
The rates are good, though not the absolute lowest, but it is the only card I know which you can use both here and abroad with access numbers in most countries.

Consumer Reports listed the one that you buy at Costco as the cheapest. There are local numbers from most European countries.

I agree with Jed. We always use the Costco calling cards.

Another vote for Costco card. I used it just recently in the Czech Republic, Poland, Hungary and Austria with absolutely no problem and very simple to use.