Project Gutenberg contains numerous books about and sources from the classical era. It offers translations from and a few original latin and greek texts. link to Project Gutenberg
Another source for translated sources (both latin and other languages) is fordham.edu.
Despite giving acces to tons of translated latin sources, the net doesn't seem to offer a wide variety of original latin sources. The current situation for greek sources (or any other language) seems to be even worse. At the sites mentioned, you're unlikely to find non-famous authors, whereas the quality of the translations and the critical apparatus may differ heavily from text to text.
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