var d = (new Date()).toString().split(' ').splice(1,3).join(' ');
document.write(d)
To break it down into steps:
(new Date()).toString()
gives "Fri Jun 28 2013 15:30:18 GMT-0700 (PDT)"
(new Date()).toString().split(' ')
divides the above string on each space and returns an array as follows: ["Fri", "Jun", "28", "2013", "15:31:14", "GMT-0700", "(PDT)"]
(new Date()).toString().split(' ').splice(1,3).join(' ')
takes the second, third and fourth values from the above array, joins them with spaces, and returns a string "Jun 28 2013"