If you've ever bought or sold a house, you (or your real estate agent) probably put together a list of comparable houses which sold recently in the same neighborhood, as a way of helping you understand typical pricing in your local market.  This information (combined with your knowledge about the difference between your house and your neighbors') allows you to set an appropriate price.

Similarly, I hoped to find enough similar recent domain sales to get at least a ballpark estimate of the premium domain market.  In this case "in the same neighborhood" (which is key, because I don't care about the price people are getting for xgadfga3.tv) meant short english word names... which I was hoping sold for more.

It took me awhile to find such a list (long enough that I began to gather the data by hand).  The online auction sites don't seem to like to share their own sale prices, but Domain Name Journal lists the biggest sales of the year.  This was very helpful. 

Our domain didn't seem as marketable as they year's top seller porn.com ($9 million) or seniors.com ($1.8 million) but it did seem very comparable to clock.com ($175,000, Moniker, 7/3/07), pottery.com ($150,000, Sedo, 7/3/07), fountain.com ($95,000, Moniker, 7/3/07), and cushion.com ($75,000, Private, 7/10/07).  All are singular, generic, single word English nouns.

Bingo.org!

Several other lists I found useful for comparison, were Zetetic's list of all-time top domain sales (for some very high numbers), as well as two searchable databases of domain sale data, DNSalePrice.com and NameBio.com.  I found NameBio.com a little more helpful, but apparently, DNSalePrice.com contains more information about private sales, so consider checking both.