Call Global Variable in Angular Expression

These expressions are evaluated against the current scope. If you have not set them in your scope via a controller, it will not evaluate. See http://docs.angularjs.org/guide/expression

Example:

function MyCtrl($scope)
{
   $scope.apiRoot = apiRoot;
}

HTML:

<div ng-controller="MyCtrl">
   {{apiRoot}}
</div>

As has been mentioned, while the above example works, it is not reccommended. The better way would be to set these variables in a service and then get them through the service.

function MyCtrl($scope, apiRootService)
{
   $scope.apiRoot = apiRootService.getApiRoot();
}

The service:

angular.module('myServices', []).factory('apiRootService', function() {
    var apiRoot = 'http://localhost:8000/api',
    apiUrl = apiRoot,
    apiBadgeUrl = apiRoot + '/badges',
    apiLevelUrl = apiRoot + '/levels',
    apiBehaviorUrl = apiRoot + '/behaviors',
    apiTrophyUrl = apiRoot + '/trophies',
    apiUserUrl = apiRoot + '/users',
    apiWidgetPreferencesUrl = apiRoot + '/widgetPreferences';
    return {
      getApiRoot: function() {
         return apiRoot
      },
      //all the other getters
   });

The best practice is to move apiRoot to a Service and inject that service into your controller. See here.

Another way to do this would be to add your global's to the $rootScope. You can do this by adding the following to your app module definition

angular.module('myApp', ['ngRoute'])
    .run(function ($rootScope){
        $rootScope.myAPI = {
             apiRoot: 'http://localhost:8000/api',
             apiUrl: apiRoot,
             apiBadgeUrl: apiRoot + '/badges',
             apiLevelUrl: apiRoot + '/levels',
             apiBehaviorUrl: apiRoot + '/behaviors',
             apiTrophyUrl: apiRoot + '/trophies',
             apiUserUrl: apiRoot + '/users',
             apiWidgetPreferencesUrl: apiRoot + '/widgetPreferences'
        }
    });

While a service does work, the angular documentation recommends against this. http://docs.angularjs.org/misc/faq

Conversely, don't create a service whose only purpose in life is to store and return bits of data.