Other
Phmc: Paleoindian Period: 16,000 to 10,000 Years Ago
A good description of the theories behind the various migration routes into the Americas, the evidence for pre-Clovis culture in the eastern part of America, and a discussion of the paleoindian sites particularly in Pennsylviania.
Nature Research
Nature News and Comment: Ancient Migration: Coming to America
A May, 2012 news feature from Nature magazine looks again at early migration theories that brought man across the Arctic to America. Was Clovis man really the earliest?