I tend to reject the notion of a universal canon, because so many different people say so many similar things that just knowing one provides good knowledge on others. Additionally, there is no sharp line of "educated". A person should be familiar with philosophy, history, the social sciences, and the hard sciences, but that's it. And the important ideas in the last two tend to be less timeless than in other fields.
There is only one book that I would suggest, and that is the Christian Bible, and the reason behind that is because a lot of Western literature, and philosophy has been written in reference to the ideas in or stemming from the Biblical text, with a number of historical happenings being influenced by Christianity as well, and this even includes secular philosophy as allusions to Biblical groups and characters is often found in Western non-Christian writings. However, a person can still be incredibly and highly educated without knowing much about the Bible, it is just more difficult to get a lot of issues.
Beyond that, I would just suggest being somewhat familiar with the following schools/groupings of thought/subjects:
Skepticism
Pragmatism
Existentialism
Postmodernism
Idealism
Analytic philosophy
History of economic thought (with familiarity with modern Neoclassical economics but more emphasis on Austrians/proto-Austrians, Marxians, Institutionalists, and New Institutional economics)
Political philosophy (The following broad categories are good to be exposed to: classical liberalism, libertarianism, liberalism/progressivism, conservatism, anarchism, and legal philosophy)
Western theology
Calculus and statistics and other moderately advanced mathematical methods
Basic physics(the sort that will overlap with metaphysics)
Evolutionary theory
Psychology and Neuroscience and perhaps philosophy of mind
History of ideas
History in general
This is just my biased list of topics, and in them, there is basically no core at all.
EDIT: wanted to further adjust political philosophy section
Last edited by Awesomelyglorious on 10 Nov 2009, 10:02 am, edited 1 time in total.