Scribd just announced a service that will sell ebooks in PDF and ePub format and they will apparently add Adobe DRM for you if you want. The service is new, and Scribd seems much more PDF orientated than ePub.
The other alternative is MOBI, and you can add DRM using MobiPocket Creator. However, you then have to upload either to mobipocket.com or to Kindle DTP as a "publisher" and the author's cut isn't very high. Note that if you upload a non-encrypted (non-DRM) MOBI to Amazon DTP the Kindle ebook will be DRM-free.
The DRM from Adobe and MobiPocket is very easy to strip using scripts easily obtained from the Internet. Popular books available in paper form only are also available as computer files, either scanned or scanned and OCRed. Overall DRM just annoys your readers.
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