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My business visa charges a 3% currency conversion fee and they couldn't tell me what the exchange rates are based off of so this wasn't a good option.
My Personal Amex charges a 1% currency conversion fee and I get 1% cash back making that fee a wash. My personal Amex's exchange rate is based on the numbers published in the Wall Street Journal. I'm sure there are also cards out there that have 0% international currency conversion fees.
By using the right mix of financial tools I was able to save 2.6% on my international buying. Ultimately the merchants who take credit cards get screwed with all this stuff, but until something changes and we have some disruptive technology from startups like dwolla.com, hold on to your wallet.