<select ng-model="url" ng-options="x.url as x.site for x in sites">

<option value>--</option>

</select>

var app = angular.module('myApp', []);

app.controller('myCtrl', function($scope) {

   $scope.sites = [

        {site : "Google",key:"607708250695616096", url : "http://www.google.com"},

        {site : "Runoob",key:"302", url : "http://www.runoob.com"},

        {site : "Taobao",key:"303", url : "http://www.taobao.com"}

    ];

    $scope.url = "http://www.runoob.com";

});