I did this using 2 very popular ebook directories. So I thought I would publish a more complete list of places where you can submit your ebooks.
Now, keep in mind that this is not a comprehensive list. Instead, it's a list of the very best ebook directories (i.e. the one's that will bring you the best results.)
*** http://www.changethis.com/ - ChangeThis.com is much more than just a traditional ebook directory. They publish manifestos. The original idea behind ChangeThis came from Seth Godin. This site can bring your content LOTS of extra exposure, but it must be extra good.
You can also submit your ebook to popular document sharing sites: