Not sure if this post breaks list rules - as Adler, who wrote this textbook, has been dead for over 150 years........The Latinum Podcast is a free online Latin audio course, which essentially simply has put this textbook into audio - designed for home school and distance learning - Latinum first went online in early 2007, and since them, has clocked up over 2.5 million audio file downloads, with thousands of regular users using it to learn Latin across the globe.
Latinum is based around George Adler's "A Practical Grammar of the Latin Language for Speaking and Writing Latin", which is available as a free pdf, or as a softcover reprint.
The course also offers a wide array of subsidiary materials in addition to the Latinum course materials - audio of Latin texts, material to help learn how to recite Latin poetry, a huge vocabulary learning section, and a selection of easy stories read in simple Latin, etc.
Users have reported that this course is helping them get to grips with Latin very rapidly. The course treats Latin as though it were music, each gradual step in the progression is achieved by playing the linguistic equivalent of musical scales, with hundreds of questions and their answers in Latin. The entire course uses this question-answer format.
The course also has extensive written materials to accompany the audio course, in addition to the textbook.
http://latinum.mypodcast.com