With the coming of HTML5 at least one new approach is added to the possibilities: the use of the input of type 'email' which allows validation on the client side. Current versions of Firefox, Chrome, Safari and Opera do support this (and other browsers just treat it like type=text, so it can be used without problems althoug then you don't have validation of course.)

It can never (as is pointed out a few times) guarantee a workable address, but it may be very beneficial (and eventually replace the server side check) in places where you just need to catch likely user errors.