Email coupons are far from revolutionary, but the thing I like about this one is that they host their coupon image on their server, and then swap it with an “Expired” image whenever the expiration hits.

That way, nobody can accidentally download and print a coupon that was no good. Image swapping – don’t you wish you could do that with newspapers? You could actually create some-what personalized email coupons using a little merge-tag creativity (here’s a tutorial).