American Polity

It seems to me that Aristotle would be rather pleased with the sort of government we have in the modern United States. For example, he favored giving the rich a greater voice in politics (so as not to treat unequals as equal), which -- despite the best efforts of John McCain -- is the case in modern America. He believed strongly in the need to have a broad formal franchise, in order to keep the masses from rebelling, but he hoped to set up the system so that only the rich and "good" would have the practical opportunity to get involved. The low level of voting shows that we've managed to create a system where, though everyone technically can vote, only half of us find it worth the bother (and voting in the US is far less of a bother than the forms of participation that Aristotle envisioned). He was full of praise for the middle class, a sentiment appropriate to a country where everyone thinks they're middle class and politicians pander relentlessly to that. And he thought the best states were those dominated by rural people, which parallels both the structural (the electoral college and Senate give Wyoming and Montana outsized influence) and rhetorical (people from the rural heartland are real Americans, unlike those urban elites) features of American politics.

Of course, Aristotle would have some disagreements with our system, notably our lack of slavery and formal gender equality. He'd also find our praise of "hardworking" people baffling, as John Kerry on a skiing trip is more his idea of a good politician than George Bush cutting brush on his ranch.
UPDATE: I forgot a key point. Aristotle favored forcing the best people to hold office whether they like it or not, so he would have found the self-promoting campaigns we have to be unseemly.