* The Latin Library (TheLatinLibrary.com): This is a good starting point and offers a substantial collection of Latin texts online, freely available. It's easier to navigate than some others, but its completeness varies depending on the author.
* Loeb Classical Library Online (though it requires a subscription): If you have access through a university or library, the Loeb Classical Library's online version is unparalleled. It provides both the original Latin and a facing-page English translation, which is invaluable for understanding. It's the gold standard in terms of quality and scholarship but comes at a cost.
* Perseus Digital Library (Perseus.tufts.edu): This is a massive digital library containing many ancient texts, including a significant number in Latin. However, it's more of a research tool with a complex interface, requiring some familiarity to navigate effectively. It's powerful but less user-friendly than The Latin Library.
* Archive.org: This archive often contains scanned versions of older books, some of which are Latin texts. The quality can vary significantly, and finding specific works may require searching meticulously.
In summary: For a generally accessible and free resource, start with The Latin Library. If you need the highest quality texts with translations and are affiliated with an institution with access, the Loeb Classical Library Online is supreme. For a powerful but complex search across a wide range of ancient materials, explore Perseus. Finally, Archive.org is a wildcard that might uncover some treasures but lacks organization and consistency.