When your website means business.

Custom Admin | Type: CSSCustom Login Logo

Add other styles as necessary

function my_custom_login_logo() { 
echo '<style type="text/css"> 
h1 a { background-image:url('.get_bloginfo('template_directory').'/images/custom-login-logo.gif) !important; } 
</style>'; 
} 
add_action('login_head', 'my_custom_login_logo');