christianj - I have a UK issued Plat Amex, which has Priority Pass membership as one of the perks. Each country has different benefits, so you would need to check with Amex in the US as to whether you qualify for one too.
Wherever you live, you can pay for a Priority Pass - see their website (prioritypass.com). It is not exceptionally cheap, unless you can persuade your employer to pay, but if you fly enough in economy then it may pay for itself.