Yes, have to agree here that some place like the UK would be a good first time overseas trip for someone in the US.
Though if one wants to take even more baby steps first (perhaps for a hesitant spouse), a couple of trips to Canada might be in order. One to Toronto or Vancouver or other place in Anglophone Canada, then one to Montréal or other place in Québec.
Actually being from Toronto I find Quebec City almost more foreign than my favourite city to visit: Munich. I've forgotten all my high school French so it's a bit of an adventure visiting there. Nice city to visit and the locals like Americans a lot more than Torontonians.
