Smashwords will do it for no charge, taking only a small percentage from net sales once your books are published. From the Smashwords website:
Publishing on Smashwords is as easy as 1-2-3:
Step 1: Carefully format your manuscript as a Microsoft Word .doc file per the guidelines in the Smashwords Style Guide and, if you desire mainstream distribution via Amazon, Barnes & Noble, Kobo, Sony and other retailers, study the guidelines for inclusion in the Smashwords Premium Catalog. Apple and Sony require ISBNs, which you can acquire from our ISBN Manager.
Step 2: Click Publish on the home page and follow the simple steps to publish your book instantly
Step 3: Read the free Smashwords Book Marketing Guide for valuable book marketing tips!