http://librivox.org/
What Project Gutenberg is to e-books, LibriVox is to audio. While Gutenberg relies and volunteer hours to scan and convert public domain texts into digital documents, LibriVox relies on volunteers to read public domain texts and compile them into listenable audio formats.
LibriVox is searchable, though the search results are not as easy to muddle through as I would like. Obviously, when dealing with public domain texts, the contents of the LibriVox library will be texts that were published prior to 1923. The individual record for a title contains links to related text files, including Gutenberg and Wikipedia. The audio itself can be downloaded in its entirety as a .zip file or individual chapters. Since LibriVox relies on volunteers who read, edit, and compile the audio tracks, a book may have many different readers.
Formats include the ubiquitous MP3 and the not so common Ogg Vorbis. This latter, the .ogg file type, is playable on many devices. While most people continue to associate audio file types with MP3, that particular file type was eclipsed by superior file types, including the open source, patent free Ogg.

http://illinoisharvest.grainger.uiuc.edu/fulldisplay.asp?cid=2797
The University of Illinois is only an hour away, and within the hierarchy of the University Library is the Rare Book and Manuscript Library. It's a place I want to visit, if only to hold a piece of history in my hands. The Rare Book and Manuscript Library has books and manuscripts from hundreds of years ago, and if you fill out the proper paperwork, you can even handle these rare objects in their reading room.
For those of us who don't have a day to make a trip down to Champaign and look at these manuscripts, the University Library has created a digitization project called "Project Unica." A "unicum" is a sole surviving book, and the Rare Book and Manuscript Library has many unica in its collection. As of this writing, 204 of these rare books have been digitized. The contents can be downloaded as low-res PDFs, high-quality PDFs, or viewed directly within your browser using the "Page by Page Navigator." This last works very well for casual browsing.
While many of the titles are in other languages, all are intriguing. It might just be better than holding the real deal in your hands -- at least you don't have to worry about damaging it!

http://www.baen.com/library/
Full texts of various Baen books (science fiction and fantasy) available in a variety of formats for zero cost. The catch? You will probably prefer the print copy and decide to buy one. Or, since the available books are the first of a series, you may wish to read the further adventures of, say, Paksenarrian the sheepfarmer's daughter, and will hunt down the remaining books in the series to read what happens. This strategy is not unlike the many free massive multi-player online role-playing games, where the initial game play has no cost but extra features (a horse, for example) will wind up costing you.

www.forgottenbooks.org
Forgotten Books has a goal of keeping old books in print. They do so by offering their books in three formats: low quality PDFs that are available online for free, high quality PDFs that are available online with membership, and printed editions that are available through Amazon.com. As of this writing date, there were 9,929 books available with 5,246 in progress (What "in progress" really means, I don't know; have they actually prepared those titles, or simply counted the titles sitting on a shelf waiting to be processed?).
The low quality PDFs look pretty good when you open them. Then you read the fine print that explains that what you are really seeing in the first fifteen pages is really the high quality version; everything after page fifteen will be the "real" low quality. Additionally, vertical striping has been added to the files to deter others from printing and selling the books. The low quality PDFs would be useful only for reference. The scans are significantly harder to read, with multiple vertical stripes and distorted characters. Since they are downloads, they can be read offline using Adobe's Acrobat Reader or an alternative PDF viewer, but the quality makes it difficult to do so.
The high quality PDFs come at a cost: Forgotten Books charges a one time lifetime fee of $49 for up to 10 book downloads per week, or the "booklover" package, $69 for up to 100 downloads per week.
The last option for acquiring books is to backpedal to the print version, which is created through Print On Demand technology at Amazon.com. We have a title from Forgotten Books collection at the library. The book is paperback but sized around the same size as a standard hardcover. The book's quality appears every bit as good as a direct publisher trade paperback title, and the price was significantly less than I expected from POD technology. To me, however, there is an issue with the typesetting. As I look over the book, I can't help but feel I'm reading from the default template for Word 2007: the typeface is sans serif, the spacing between lines is just over single spacing (Word 2007 sets this at 1.15), and there is another space between paragraphs.
Forgotten Books divides their titles into two series: the Easy Reading and the Classic Reprint. The Easy Reading books appear to have been reformatted from their source material (resulting in the format I described above). The Classic Reprints are simply reproductions of titles as they appeared originally. This is not a new practice; I have a copy at home of Gypsy Sorcery and Fortune Telling that is a 1980s reprint of the original Charles Godfrey Leland text from 1891. Although the binding and the book cover were new, the contents were nothing more than reproductions of the original publication.

http://www.elfquest.com/gallery/OnlineComics3.html or www.elfquest.com (in case the direct link to the collected comics doesn't work)

www.sacred-texts.com
Sacred Texts is the only stop you will need for texts associated with religion, mysticism, plus every permutation you can imagine, and even some you can't. Aside from religious texts, it also includes a variety of literature, legends and folklore like Arthurian legends or Norse tales. There is probably more reading available at this website than a life-time of reading and scholarship could digest.
Typically the editions are in the public domain, but there are some files that are copyrighted and noted as such. In contrast to Project Gutenberg, which provides plain text files of its titles, Sacred Text's titles are formatted in HTML with hyperlinked tables of contents. The books are intended to be read within a web browser. The disadvantage to this is that reading within a browser window is difficult when using the page up and page down buttons. The advantages are that the entire text of every book are searchable from search fields (you could even, say, search from Google using a site search: "Lance of Longinus" site:www.sacred-texts.com).
Daily additions of new material make this site worth bookmarking to revisit regularly.
Advertisements on the site will appeal to you to purchase a copy of their newest DVD, which is basically a snapshot of the site to be used for local or offline reading. It does not contain the newest material. Icons attached to each entry clearly indicate whether the book is on the latest DVD (shows a disc icon) or too new to be included (shows a New! logo).

www.gutenberg.org
One of the great treasures of the digital world, Project Gutenberg showed us what ebooks could be. Accessing these plain text ebooks is like purchasing the Britannica's Great Books of the Western World collection -- except without the $1000 price tag or the wall of shelves.
Gutenbergs books exist in their essential ASCII, which means the words are distilled into their essential typographic characters; formatting need not apply. There are some titles, Carroll's Alice books, where either Carroll's own illustrations or Tenniel's illustrations are an essential part of the reading experience. But for many titles these flourishes are nothing more than embellishments and decorations.
Gutenberg has a variety of file types available for each entry. A standard book entry will include "Hand-Crafted Files," those files that were generated through the work of human volunteers, and "Computer-Generated Files," converted versions of the Hand-Crafted Files into different file types. Hand-Crafted Files include HTML or plain text version in either uncompressed or ZIP archives. Computer-Generated Files include EPUB (which as of this date appears to be the most widely accepted ebook format), Mobipocket, Plucker, and others. Clicking on an uncompressed file type will load the text into the browser window, but optimum reading should be done in another application such as Stanza or yBook. There are even audio versions of many books that are machine read. I'm not fond of these, and don't believe they will really take off in popularity until the personal computer acquires intelligence and decides to listen to audiobooks in its free time instead of watching its own screen saver. They sound rather like Hal2000 reading you a bed time story.
Each book contains fine print (without formatting it retains the same size as the remainder of the book's text) about copyrights. The majority of Gutenberg's titles are in the public domain. The remainder are titles that have not had their copyrights renewed (such as a short story by Kurt Vonnegut), or have been made available with some restrictions by the authors (The Cyberpunk Fakebook).
True, my inner nerd misses the truly impressive sight of a wall full of leather bound classics. And carrying that collection of three thousand classics in EPUB format on a thumb drive just doesn't pack the intellectual punch of a tattered copy of Moby Dick. But ease of access makes up for these inadequacies, and the price really appeals to my thrifty nature.