For many years now, there has existed a website called Political Compass. This site purports to place people on a graph of the space of political opinions, on the basis of their answers to a set of questions.
PC.org is at best naive and at worst a fraud: the axes (economic and social "self-government") presupposed are not necessarily orthogonal, independent of each other or the most important discriminant of political allegiance, and the questions employed to ascertain one's views are hopelessly biased - you have to sign up to some pretty nasty stuff to avoid being a social self-government fan.
For me the biggest problem with this site is that people quote it authoritatively as though it were some objective public-spirited Internet service as neutral as the Currency Convertor. It's not. It's little better than a party political broadcast for the Libertarian Party (amusingly, the site does not answer the psephologist's question as to why the US does not have three major political parties if it two major political axes rather than one).
Much to be preferred is the HowToVote.co.uk, which takes extracts from party political manifestos, tots up which party best represents your views on each set of issues and overall, and tells you how you should vote if you wanted to reflect that. An advantage of such a system is that it is a posteriori, not predicated on some hypothetical model of the structure of political ideas. Needless to say, in the 2001 election it told me I was Lib Dem on basically everything except Education and Foreign Policy, where I was supposedly a Tory, and I voted Labour nonetheless. Education policies have now changed - I suspect my support for graduate taxes swung the site's assessment towards Tory, and I find that the Lib Dems represent my views on most things best, apart from constitutional affairs, where they are still the Devil's Party after 400 years (it'd be nice to see a 1622-1922 version of PC.org which took "High Church / Low Church" as its main axis for political allegiance).
Why is it that the only people who agree with me on constitutional affairs are justices of the Bundesverfassungsgericht or the loons in the UKIP?