I am brand new to laravel and am setting up admin panel authorization on my first application. The way I have my files setup currently setup is:
controllers/
In your admin/login route you have an unnecessary return before the Auth::logout() call, nuke that and it should fix it up.
Another issue here is that only your one 'admin' route is getting filtered. You could wrap all of your admin routes with a Route::group() and apply the 'auth' before filter or you could use Route::filter('pattern: admin/*', 'auth') too.
Check out:
http://laravel.com/docs/routing#filters
For the second issue, is your Admin Dashboard controller class named Admin_Dashboard_Controller and if so, do you have an action_index() or get_index() function in there returning a view?
Check out:
http://laravel.com/docs/controllers#nested-controllers
(I'm assuming you're using L3 here btw.)