I’m not an Augustine scholar but in my research and teaching I occasionally have a need to check a text of Augustine that I don’t have a copy of. A few years ago I came across the Italian site augustinus.it and have made profitable use of it. The site, sponsored by the Italian publisher Città Nuova, offers all of Augustine’s texts in Latin and Italian in an html format. Not long ago Città Nuova also completed the hard copy edition of Augustine’s Opera Omnia in Latin/Italian, which amounted to 70 volumes or so. (Here’s a blurb about the series on the Città Nuova site.) I used some of these volumes back in the 90s and recall that they were very well put together with extensive notes.
The resources at augustinus.it are vast but I don’t have time at the moment to provide a list. Probably the most useful of these resources is the search engine, which allows users to locate words and phrases across all of Augustine’s Latin texts. The Italian texts are also searchable and they are working on putting up the texts in Spanish translation too. A few dozen are already available in Spanish.
Limited areas of the site are in English, Spanish, French, and German. Here is the welcome page for English-speakers.