A “List of Germanic Peoples” is available on Wikipedia, as is a deal of information on various ancient tribes and tribal lands. Adding more Sources (books) of my own, I have begun mapping the ancient tribes. A more informative list can be found if you scroll down the sidebar to he section called Ancient Northern Tribes A-Z.
The Norse/Germanic speakers of Scandinavia and Northern Europe began to expand widely from around 200 BC, and a Migration Age begun which changed history and led to the downfall of the Roman Empire. There have been many speculations as to what reasons there were for the Migration Age - overpopulation and poverty was once the most popular explanations, but now the bit about poverty seems to be challenged by the archaeological records -- it seems that material surplus which could finance great tribal migrations was a more likely reason. Their military success had to do with the way all boys above the age of fifteen was per definition a warrior and a soldier in the tribe that was an army -- with women and children travelling with the army that was a tribe, offering support in many ways.
But why? Why this need to migrate? One reason that will be touched upon in some article are the many legends the Germanic tribes themselves had of beeing flooded -- and geographical history has shown that the shores of Scandiavia and Northern Europe have been flooded by rising waters and great tsunamies several times in prehistory, forcing the tribes to move into the continent. Modern maritime archaeology confirms that countless cultures were washed away as sea Levels rose and covered formerly dry lands with Ocean.
Here follows a list of the tribes I have covered so far. Below that are links to a very good series on the Germanic Tribes.
Germanic Tribes Documentary Series: