Here's just what I notice in my travels:
In America the conservatives lean authoritarian because of a long military tradition. I won't go so far as labeling them 'imperialist' but they certainly tend to view America as necessary for the security of democracy and free trade. The "defense of liberty" is their main concern, and the military tends to be the biggest government institution they support, along with law enforcement and finally public education systems. The liberals here lean libertarian, which in this context tends to mean more government oversight of the economy and spending on domestic problems, infrastructure, welfare, and leaving other countries to do their own thing. The liberals tend to be centrist on the global stage, and by no means socialist, although many support some mild form of socialized medicine.
I like to think that many Americans are center-right, and a lot more libertarian than the politicians we vote into the legislature. That is, citizens want our government to start dealing with the problems at home, and less abroad, or at least that's the trend.
Unfortunately, typically credible grassroots movements tend to get hijacked by our two-party system. The Republicans are hijacking the much more libertarian and fiscally conservative Tea Party Movement right now. In reality, both parties spend enormous sums, and the only difference is their budget priority.
Because of the 60 votes in the Senate necessary to pass any non-fiscal legislation, and excessive lobbying of corporations, there is little room for a third and fourth party, which in my opinion is unfortunate.
Interestingly in the UK it seems to be the case of authoritarian liberals and libertarian conservatives. A classic case would be net neutrality and the DMCA bill that just passed over there.
Also, the BNP is just whack.