Without a doubt, one of the best desk accessories I have is a custom made address embosser. I originally purchased it for use stamping my return address on my wedding invitations and ever since, its left a beautiful mark and lasting impression on any correspondence I send.
I actually have two embossers in my arsenal - one rectangular and the other is round. Since we recently moved into a new apartment, its now come time to update my plates.
Figured to share some of the places I found online that will sell you the plates, since the embosser itself can be used indefinately.
For rectangular plates, a great choice is Paper-Source. They offer address plates with 15 font choices (Filosofia anyone??) for $31.50. Looking for a motif or a custom monogram? They also carry a line of circular plate designs, all for the same $31.50 price.
Wilshire Graphic Press offers replacement plates as well. You can choose from their list of standard typefaces or email them a font of your own choice for a $10 surcharge. If you want to provide them with custom artwork, the charge for replacement rectangular plates is around $45.