https://www.textkit.com/ - This one is great for Classical Greek as well. It has a bunch of free textbooks in their entirety.
http://www.linneyslatinclass.com/ - The focus is on Classical, rather than Ecclesiastical Latin, but it still gets the job done and there are a ton of audio clips. Note that the textbook used for this class can be downloaded free online (link on the website) or purchased for around $15 on amazon. The author of the site also writes and sells his own book, Getting Started with Latin, which he sells on http://www.gettingstartedwithlatin.com/. That site also has free audio links for both CL and EL, though they correspond to his book and not the above free class.
http://www.lingvalatina.com/ - Tons of exercises and audio, but you need to buy the Lingua Latina books (Familia Romana and/or Roma Aeterna) separately to get any benefit out of it.
If you don’t want to spend any money, the first two websites are your best bet.
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.