Head vases are sold by the hundreds every week on Ebay.  Since they make an interesting topical collection for people with many interests, they stay popular.  They are frequently inexpensive so you can afford to collect headvases which reflect your individual interests; cats, people, entertainment figures, Disney or anything else you enjoy.

As I get ready to develop HeadVases.com I rechecked Ebay and there are just over 1,000 auctions currently running that have "Head Vase(s)" in the title.  I have also learned to use the Google keyword tool to get a better idea of how people search for headvases on sites other than Ebay,

Head Vase is the most popular term with 590 monthly searches

Lady Head Vases had 590 plus 260 more for the singular

Antique Head Vase had 110

Napco Head Vase had 73

Vintage Head Vase had 46

There were some other categories with less than that.  The entire list is long but I also see some searches such as Horse Head Vases that make me think there is a subset of collectors who are interested in horse collectibles, not head vases themselves.  That could be a topic all it's own.