When I was a teenager, the Georgia O'Keeffe poppy stamps came out just after I purchased a set of matching cards at the Metropolitan Museum of Art gift shop. I can still remember being excited about combining the two and wondered if anyone would notice. Then, when mailing out my wedding invitations some years later, I spent a little extra postage on each card just to have a matching stamp (my dad totally rolled his eyes at this one, and rightfully so!). So you see, my keen interest in beautiful stamps has been going on for some time and is likely never to wain. And while all of the stamps in this particular set aren't up my alley, there are some that are just stunning (like the O'Keeffe). You can use ones you don't love for bills :)
You can buy these stamps in sheets of 10 online or at your local post office.