I would second Schin's recommendation heartily. The people at Atelier Gargoyle are outstanding and the wax is lovely.
Looking at this video, I would make one comment. See how the seal sticks to the wax after impressing it? This can be lessened by breathing heavily a couple of times on the face of the seal (thus putting a little moisture on it) just before dipping it into the hot wax. If you are doing multiple impressions, have a moist towel over a piece of ice to both add moisture to the seal and keep it cool, and rest the seal on it momentarily between impressions. A hot seal tends to stick.
WARNING: Reading further in this post may tempt you to endanger your purse.
A request was made earlier in this thread to see some of the seals we have. Here are my two favorites.
A couple of years ago, I bought an unengraved gold watch fob made in Birmingham, England in the year of my grandfather's birth (1894). On one side the stone is bloodstone, the other is cornelian, both common to engrave back in the day. I thought, it would be great fun to have both sides engraved to make wax seals. I was in touch with Schin at this time, and she also was considering having a seal made for her calligraphy business, and we were both looking at Dexter Rings, a small company in England, that did the finest work I had ever seen. After much consideration (due in no small measure due to the price of such work), we both went ahead with the custom seal idea--Schin designed her seal for OpenInkStand, and I chose two of my favorite statues from my collection, photographed them, and sent the photos to Dexter, where master engraver William Wright engraved the stones using my photos as a guide.
I still marvel at his skill every time I use the seals. They are about 22 mm in diameter (so, say the size of a quarter) and have such nice detail. I have my heirloom.
If you are looking for a seal in a hurry or something inexpensive, you won't find it at Dexter. Mine took 6 months to make and my purse was reeling after the exchange. It was, though, worth the wait and the money.
You may visit Dexter Rings at this website if you dare:
http://www.familysealrings.com/