General

• Ancient Greek Philosophy via Galaxy.com
• Ancient Philosophy via Philosophy Research Base.

Specific

PreSocratic Philosophers

Classical

• The Sophists (subject to IP verification)
• Plato.   English Texts.  
• The Last Days of Socrates
• Aristotle.  English Texts.  

See Perseus for Greek texts of Plato and Aristotle.

Post-Classical

• Stoicism
• Epicurus & Epicureanism
• Epicurus.info 
• Ancient Skepticism