One of the most important resources on the internet, this site not only provides content and is well organized, it also features "The Wayback Machine" which serves as a date-sorted collection of websites, especially and including sites which no longer exist. Very useful when looking for content from a website that has changed over the years. And the fact that this site doesn't charge for its content is amazingly impressive.
This website contains lots of public domain downloads -- not just text but also PD movies and sound. Their old time radio collection has lots of entries. Search for the Old Time Radio Researchers Group (OTRR) recordings for the best ones -- you can download complete seasons with recorded introductions.
Thanks to this site we were able to recover a new customer's website that had been lost when their password was compromised. This site helped save a new customer money and time and made us look like rock stars.