ShareyTee:
I was just thinking of doing the same thing. I have 3 full shelves of books going back to the 50s. Even though I am still an active (barely) JW, I rarely use most of these books anymore, they are collecting dust. I want to get new book shelves AND new books, but need to get rid of most of the WT stuff first. (I have the WTCD, even though I know the Borg probably altered some of the old text to suit "New Light".)
Some time ago, I thought there was a site called "Bethel Antiquities" but the closest I found through Google was the previously referenced "Free Minds Antiquarian", but I find no reference on selling books there. (Anyone where they BUY their literature FROM and how we can SELL ours?)
There are sellers on EBay as mentioned.
I have had excellent success selling college text books on Amazon.com Marketplace. I see that there are some bound volumes for sale for $19.95 and up. You can add yours but I cant say it will sell fast on a site not specializing in WT literature.
SnakesInTheTower (of the "not reading the old WT S*HT anymore" Sheep Class)