As mentioned above, this one is good enough if you ask me.
var regex = /^([a-zA-Z0-9_.+-])+\@(([a-zA-Z0-9-])+\.)+([a-zA-Z0-9]{2,4})+$/;
But if you don't want the domain ending (.com, .nu, .net etc) to contain numbers (which is my prefered choice) the edited version would be :
var regex = /^([a-zA-Z0-9_.+-])+\@(([a-zA-Z0-9-])+\.)+([a-zA-Z]{2,4})+$/;