The Georgia Ornithological Society is selling the Migratory Bird Hunting and Conservation Stamp (aka Duck Stamp) and holder for $15.
If you recall, I got schooled by Paul Baicich that these tags fit easily on binoculars and make very little noise and don't get in the way of your bird viewing pleasure. For those who still aren't convinced, they do also make great zipper tags.
This is one of the cheapest, most effective purchases you can make to buy up habitat for all kinds of birds. And with the decline in duck hunters, birders really need to step up to the plate on this one. Over 98% of the money for the stamp actually goes to purchase habitat and less than 2% goes to administrative costs, this is very worthwhile.