Free sites to advertise permafrees

I finally decided to take the plunge and go wide with some of my books, and I made The Working Chicken free on all retailers to prime the pump. After listing the freebie plus two paid books, begging my readers for reviews (and getting a sprinkling here and there), I sat back...and watched as nothing happened. In the last two weeks, I've made three sales on Nook and none anywhere else --- not unexpected, but I clearly need to put in a bit more effort to get things moving.

I figured the next step was to list The Working Chicken on various advertising sites. I opted to start with places I didn't have to pay for, using the handy sortable list at http://www.readersintheknow.com/list-of-book-promotion-sites to find my options. However, most of those sites don't allow you to give links to any retailer except Amazon. Without paying for a listing (or signing up for an account), the only sites I found that will list other retailers are:

http://contentmo.com/submit-your-free-ebook-promo
http://ereadergirl.com/submit-your-ebook-2/
http://freebooksy.com/editorial-submissions
http://readingdeals.com/submit-ebook/free
http://www.thereadingsofa.com/authors.html

I guess the next step is to determine whether it's worth paying for listings for The Working Chicken. Of the low-cost paid advertisers, which ones do people recommend for advertising non-Amazon books? I'd be especially interested in hearing from those of you who write non-fiction.