Working on a timeline after lurking arond here for along time, and interested in some input.
Without giving the POD away, what do you suppose the far-reaching effects of the kingdom of Francia never being fully established, and Charlamagne's line failing early? Specifically a -much- weaker Roman Catholic church, and none of the attempts at centralizing effects of the legitimacy the Pope's support lent Francia present.
Basically, we're talking a drastically different Europe from Iberia to the Rhine.
Just off-hand, we have:
-Obviously, a much weaker role for the Catholic church in general, but especially in the traditionally -very- Catholic frankish kingdoms, and more perhaps more interestingly, England. Which leads me to...
-A Saxon-dominated England. A Norman invasion is a hard thing to come up with when there is no Normandy.
-Also, likely no Holy Roman Empire (certainly not as we know it), and perhaps even an Orthodox Germanic populace. Do you suppose this would hasten or delay the unification of Germany, in the long run?
That's about all I can come up with while not giving away the POD too much (thought I'm sure there's a few good guesses already...). If you wish to discuss it more extensively, feel free to shoot me a PM, and I'll spoil it for you, just interested in anything I may have overlooked, for now.