Short example of how to declare services in AngularJS.

angularServices.js

//from most to least verbose, but it is all the same in the end. 

(function() {

    var module = angular.module("myApp.myModel", []);
    
    var MyModel = function MyModel() {
        this.asyncService = null;

        this.someApi = function() {
            return this.asyncService.getStuff(); //promise?
        }

    }

    var myModelProvider = Class.extend({
        model: new MyModel();
        $get: ['asyncService', function (asyncService) {
            model.asyncService = asyncService; //dependency injection
            return model; //resolved for the lifetime of app
        }]
    });

    modules.provider('myModel', myModelProvider);
}())

// or

(function() {

    var module = angular.module("myApp.myModel", []);
    
    var MyModel = function MyModel(asyncService) {
        this.asyncService = null;

        this.someApi = function() {
            return this.asyncService.getStuff(); //promise?
        }

    }

    module.factory('myModel', ['asyncService', function (asyncService) {
        //could do some stuff here
        return new MyModel(asyncService); 
    }]);

}())

// or

(function() {

    var module = angular.module("myApp.myModel", []);
    
    var MyModel = function MyModel(asyncService) {
        this.asyncService = null;

        this.someApi = function() {
            return this.asyncService.getStuff(); //promise?
        }

    }

    module.service('myModel', ['$asyncService', MyModel]); //most simple option
}())

@joelhooks
Just working for you as a second pair of eyes ;-).

BTW, rumour/documentation implies that a factory creates a singleton. Since a service (which uses new) does not necessarily create a singleton, here is a way to easy force/manage singletons regardless of .factory() or .service() instantiations.

(function(angular) {
    "use strict";

    var _service    = null,
          _singleton = {
            asyncService : function() { return _service              },
            someApi      : function() { return _service.getStuff();  }
        };

        /**
         * MyModel constructor function
         */
        MyModel = function ($asyncService) {
            _service =  $asyncService || _service;
            return _singleton;
        };
    },


    // Redefine for minification...
    MyModel = [ '$asyncService', MyModel ];


    // Register `myModel` as an instance of the MyModel service or factory.
    angular.module( "myApp.myModel", [])
           .service('myModel', MyModel); 

}(angular));