The first ‘official’ (important designation) and fully legal online gambling site is now live in the US, UltimatePoker.com. Born from recent legislation allowing individual states to authorize and regulate online gambling within their own state borders, the site is open to anyone physically in Nevada (and only those physically in Nevada). New Jersey and Delaware have similar laws and will be pursuing sites of their own I am sure. How they verify your location is a mix of IP, location of your mobile device (which you must register) and some proprietary measures. More here.