Egypt
Amarna, Nubia, Aldokkan - Ancient Egyptian Art, Egypt Images, Egyptian Galleries, Egyptian Treasures in Europe, Egyptological Homepage of Michel Malfliet, Egyptology.com, Field Museum - Cleopatra, Splendors of Ancient Egypt, The Ancient Egyptian Culture Exhibit, The History of the Egyptian Obelisks
Etruscan
ArtLex on Etruscan art, Etruscan Gallery - The Vatican 1, Etruscan Gallery - The Vatican 2, Etruscan Section, Etruscans Art (The)
Greek
Detroit Institute of Arts : Permanent Collection -, Greek Art, Greek Art, Odyssey Online: Greece, Perseus Art & Archaeology, The Metropolitan Museum of Art - Greek Art from Pr, Wikipedia: Greek Art
Mesoamerican
Aztec Tenochtitlan, Mayan Rubbings and Batik Serigraphs, Merle Greene Robertson's Rubbings of Mayan Sc, Mesoamerican Art
Minoan and Mycenean
Art of the Aegean: Mycenae and Tiryns, Art of the Cyclades and Crete, Late Minoan Painting and Other Representational Ar
Roman
Ancient Art - Rome, Ancient Rome, Images from History, Riley Collection of Roman Portrait Sculptures, Roman Art and Architecture, Roman Ceramics, Roman Glass - Reflections on Cultural Change, Theatrum Pompei Project, Villa of Oplontis
Etruscan and Roman Art : A Bibliography
Though the author says this list is neither comprehensive nor up to date - it is a good start to books covering the Etruscan and Roman art periods.
The Catacombs of Rome
Ars Mar Film describes the art of the Christian catacombs of Rome, which include frescoes, sculptures and inscriptions.