Never reply to any of them, not even on the ones that say "Click here to be removed" That will only bring a lot more. You can bock each address as it arrives by putting it on your "Blocked list" in IE and there are one or two free programs that you can download to help you do this.
Click on the "Blue" downloads link at the top of this page, you will see the ones recommended by other forum users. Keep adding them to your list and slowly over a period of time they will reduce, but you will never stop all of them, its a thriving industry!. j :o(