A zone of visa-free exceptions has been created in the Schengen area, but even there you'll need to apply for a work permit for longer stints (and the host country is obliged to give it to citizens of other Schengen countries, with some exceptions).
Nordic countries also have their own passport union, so a Finnish passport, for example, will let you go and work in Iceland or Norway pretty freely.
I would imagine there are be some other regions that have similiar agreements. I think that the Commonwealth at least used to have some benefits for its citizens, but I'm not sure how much of those remain.
[1] http://www.citizensinformation.ie/en/moving_country/moving_a...
This is possible even between Nordic countries (consider Juha Valjakkala / Nikita Fouganthine who we get to keep in Finland as Sweden understandably does not wish him to enter).