I had that happen few times; twice in US and once in UK. The toughest part is remembering where you truly used your card last, cause that is where it most likely got "snatched". Basically, how it works is this: you walk into a store, use your card, the guy behind the counter swipes the card on a machine that reads your magnetic strip and bingo, you are done. Next thing is easy... They take that information and stick it on to the card made up with any name from any bank, the key is lining up the first 4 digits of the card with the name of the bank, like 4147 is Visa from First USA, or 5124 is a Master Card from the Chase bank or 6011 Discover. The ironic thing is that after 9/11 when Patriot Act and KYC acts came into power, I wrote and sold KYC and Anti-money laundering system, so I spent months learning about little things to look out for that would make one suspicious in these things, yet I got caught literally in a blink of an eye. For me it was easy to think backwards on charges I was making and figure out where it was actually swiped. Close to $20K in charges made on the card across 3 different Home Depots in Long Island, only because my wife bought $12.00 worth of groceries in some small shop in Brooklyn.
As for what to do... The recommendations of making changes to passwords are good, contacting your banks and asking for extra protection, double passwords, secure ID cards, etc., is also good. Places like PayPal have secure keys that they can send you, so when you pay with it, you have to punch in a special number that gets regenerated every time. Also, strongly recommend contacting companies in charge of monitoring your credit history and they can help. Experian is one of them and I believe their number should still be 888-397-3742.
Finally and I strongly recommend that, contact your credit cards companies and give them your pattern usages: most frequently used stores, restaurants, Internet sites, etc. Basically everywhere where you normally shop. Then ask them to contact you if they see anything not in that pattern. I did that, although my C/C company hated me, since I spent 70% outside of the country, which made it hard to monitor. The way out of that was to always let them know when I was going out of country.
Sorry for the long rant and hope it can be of use. Crappy thing to go through and good luck!