I'll admit that I am not a user of eBay...but that might change.
In a recent article in his online newsletter, Dick Eastman showed a list of the genealogy-related items that he found for sale there. Those items included books, CD's, maps, and city directories, to name a few.
You can even set up eBay to watch for items that you specify. That is like Google Alerts, where you have Google do a specified search for you and notify you of the results via email. It does the work for you in the background, and eBay has a similar capability. Dick's article goes into detail on how to set up such a feature. (On this Blog, go to the post for 25 Aug 2009 for a blurb on using Google Alerts.)
You can read all of Dick's article at: http://blog.eogn.com/eastmans_online_genealogy/2010/01/genealogy-items-on-ebay.html