You could obviously google it and get a couple of good results but I thought someone here on DP probably knows a list of free e-book directories... Where do you submit your free e-books? (if you do)
Just found an interesting list; http://www.tech90s.net/about37.html Feel free to post your lists as well : )
upload some free ebooks to download.com i did and it was then picked up by softpedia.com and included in there site as well i have had a few thousand downloads of the ebook from both sites which is good as the ebooks contain links to my websites and my affiliate links
You can also sell them on Ebay for about $0.99. This takes a little more work but not only can you make a bit of pocket money from each sale, but you should find that the people are buy from you are much more likely to click on your links within the ebook. Most people who download free ebooks never actually read them, and just leave them to gather dust on their hard drive, but if they've paid for it, even if it is only a dollar, they are much more inclined to actually read it and therefore you should see higher click-thrus.