There are some sources online that are so well known and so widely used that I just assume everyone knows about them. Then I stumble across people who haven't heard of one. Obvious Sources are posts dedicated to those resources we should all know about.In this world of copyrights and licenses people forget one of the most valuable resources available - the public domain. Works that are old enough lose protection under the law and become part of our shared heritage and culture. At some point every book and document will become available to be read, published, folded, mangled, and/or mutilated by anyone for any reason.
Getting the books and documents off of dusty shelves an into a digital form is a huge undertaking. Google Books may be scanning books by the thousands but those are transcribed by machine and can be full of errors. The original project to type, proofread, and distribute texts is Project Gutenberg.
Since 1971 Project Gutenberg's founder and an ever changing group of volunteers have created a massive resource. We have an ever growing collection of public domain works thanks largely to the inspirational and foundational work done by the Project.
The Project Gutenberg files are mostly just text. Images are included when appropriate but the bulk of the material is simple text. No need for special software or hardware. You don't need an e-reader or a certain type of computer. However if you do have an e-reader or other device there are other sites that have taken some of the works and reformatted them for you. Feedbooks and Manybooks are two sites that allow you to read the classics on whatever device you happen to own.
If you want audio versions of these books there are a couple of options. Project Gutenberg has many works that are read by computer. Not surprisingly these are not ideal listening material. LibriVox and Literal Systems provide and ever growing list of works narrated by human beings.
There are thousands of books spanning hundreds of years that are there for the taking. Enjoy!