Viking (4)
http://www.worldheritagesite.org/categories/category39.html

Birka/Hovgarden
Jelling
L'Anse aux Meadows
Thingvellir

I would go for Thingvellir for the history of democracy and L'Anse aux Meadows for the first European attempt to colonise the Americas.

I agree with Assif. L'Anse aux Meadows and Thingvellir (which seems to pop up all the time...)

The most interesting and perhaps important, but in the end it won't make Top 200. Essentially the remains are a couple foundations of sod houses. Unfortunately, there is nothing from the Viking Age that really stands out. Sod and timber in wet climates just does not last long.

I would go only for Thingvellir

Supporting both Thingvellir and L'Anse aux Meadows

Birka/Hovgarden - NO - a bit regional. The role of the Vikings in the Middle Ages is better represented by others below
Jelling - NO - The bringing of Christianity to Scandinavia? Again - a bit too regional I think
L'Anse aux Meadows - MAYBE. The problem is that nothing is visible but I think this "cul de sac" of history is also one of the great "what ifs" and probably justifies inclusion!
Thingvellir - YES - other "Parliaments" are really far more significant in terms of World history but this does bring in an early, and "iconic" example of "democratic" self government and also the voyages of the Vikings. te

My selection:

Thingvellir

Looks like we're done with this quickly. Summarizing:

Birka/Hovgarden
Jelling
L'Anse aux Meadows - remains of earliest example of European presence in North America
Thingvellir - early, and "iconic" example of "democratic" self government and also the voyages of the Vikings