I recently attempted to construct a family tree of the Celtic deities. This proved to be much harder than I initially thought! Not only do you have to deal with a multitude of sources, but you have to filter out which sources are more accurate, and what information has been lost in the sands of time.
Timeless Myths has genealogies for several pantheons; Irish, Welsh, Norse, Greek and Roman. These were constructed from various sources and are in no means complete (and in some cases, contradict each other). But I find it helpful to see the various deities displayed in this way. It allows me to see the bigger picture and to understand the context of the many stories and adventures of the Gods.
© A Year And A Day (2013)
West Coast Pagan 
Wow! This is really cool. Thank you.