OverDrive Downloadable eBooks
Downloadable EPUB Books are now available through the library's subscription to OverDrive. To search just for eBooks, use the drop-down menu to select "Adobe EPUB eBook." (see image below)

OverDrive - Front Range Downloadable Library

Additional Classic eBooks through Overdrive - Choose from over 15,000 titles that never expire and don’t count against your library checkout limit!

Help - Basics - Adobe EPUB Books
Software Help
Troubleshooting

Compatible eBook Devices

epubBooks
http://www.epubbooks.com/
epubBooks provides a selection of EPUB eBooks for anyone to download and read for free. epubBooks does not provide bestsellers, but if you are looking for more recent titles or the latest bestsellers, epubBooks has created a page listing the more popular online stores to buy from. EPUB is a free, open standard supported by a growing number of reading devices. 

Some information on ePub from http://www.labnol.org/software/epub-format-ebooks/10879/ :
“ePub is now a standard e-book file format that is supported by almost* every e-book reading device include Sony Reader, BeBook, iPhone and the Nook from Barnes & Noble’s.” 

"Other than hardware devices, you can also read .epub books on your desktop or mobile phone using free e-reader software like Mobipocket, FBReader (for Linux), Aldiko (for Android) or Adobe Digital Editions."

"O’Reilly, Shortcovers, Sony Store are some popular book publishers that provide ebooks in ePub format but if you are looking to download classic titles to read offline, the best place is Google Books (select the “public domain only” option)."

"Firefox users can download EPUBReader, a free add-on that lets you read the contents of any ePub book right inside their favorite browser without requiring any special software."

"ePub is basically a zip file that contains a collection of text files and images. This add-on will simply uncompress that zip file and display the contents inside your browser."

"In regular course, if you click on a link that points to an ePub file, Firefox will prompt you to to save that file onto the hard-drive but with this add-on installed, the ebook will directly open inside your Firefox tab like any other web page. Additionally, you can open any ePub file that’s on your desktop using the File -> Open File menu in Firefox. All the ebooks are automatically stored in your Firefox profile under a separate sub-directory."

Internet Archive
http://www.archive.org/details/texts
"Internet Archive is a non-profit dedicated to offering permanent access to historical collections that exist in digital format. Provides over 2.5 million free ebooks to read, download, and enjoy."

Google Books
http://books.google.com/advanced_book_search
Google Books ~ “Google Books has more than a million public domain (out of copyright) books in the EPUB format that are completely free and they aren’t protected by DRM so you can read these ebook titles on any device / computer without restrictions.” (source:  http://www.labnol.org/software/epub-format-ebooks/10879/)

Also, the U.S. Government Printing Office (GPO) and Google have entered a partnership to offer the public, for the first time, Federal Government titles in an e-book format. The titles will appear on Google's recently launched Google ebookstore http://books.google.com/ebooks, which can be searched, purchased and read on any connected device with a capable browser. Currently the public can search for titles such as the appendix for the "Budget of the United States, Fiscal Year 2011", "Remembering the Space Age", and "Borden's Dream" (a history of Walter Reed Army Medical Center). GPO has about 100 titles in the catalog and will continue to add titles in the next several months. Read more about GPO's partnership with Google on the FDLP Desktop http://www.fdlp.gov/component/content/article/19-general/864-gpogoogle.

Feedbooks
http://www.feedbooks.com/
Describes itself as “A place to discover and publish e-books”

Kobo
http://www.kobobooks.com/lists/freeebooks/RYnbq2Rd7kSXf7MOhDofOQ-1.html
Free e-books available through Kobo (Note: Not all titles are free.)

Diesel eBook Store
http://www.diesel-ebooks.com/cgi-bin/gbooks/index.cgi
Free ebook download collection from Diesel eBook Store.  Free ebooks in ePub format, including classic American and British fiction, American history, children's literature, professional and research documents, and more.

bookworm
http://bookworm.oreilly.com/
a free platform for reading e-books online.
(Note: bookworm is not a source of downloadable e-books.)

Got a Kindle?
See Amazon's "Free eBook Collections" for "free classics and out-of-copyright, pre-1923 books, as well as limited-time free promotional ebooks available for Kindle."