Following up on the earlier post on the five worst U.S. allies, I thought I'd try to identify the five best.
1. Australia. Australia has been a valued U.S. ally for a long time. They have not been a fair-weather friend, and have assisted us even when U.S. actions were highly controversial, such as in the Vietnam War, and the Iraq War. Militarily they have fairly small numbers of forces, but they are highly effective. Despite being far away, Australia is probably the most familiar Asian country to Americans. And by familiar I mean, if they had to leave the U.S. permanently and settle in Asia, most Americans would probably feel more at home in Australia(or in New Zealand) than pretty much anywhere else.
2. Canada. Most Americans take Canada for granted, and that's why it is one of our best allies. Despite the fact that it shares an extremely long border with the U.S., Americans feel perfectly comfortable having Canada as a neighbor. Yes there is a strain of anti-Americanism in Canada, but it never really seems to greatly affect our relationship. Canada is a major trading partner, a good place to vacation in, and often assists the U.S. abroad. Like Australia they speak English (militant Quebecois aside), and have a society most Americans could live in without drastic changes. It's possible they should be in the number one spot, but Australia has been more active in its support for U.S. policies.
3. Britain. Another long-time U.S. ally. I believe that Britain is in decline, and that the U.S.-British relationship has deteriorated a bit, but Britain's record as a U.S. ally is so strong that it can't be left off of this list. It also has strong cultural, political, and of course linguistic ties to the U.S.
4. Israel. I know Israel is controversial as an ally, but I put it on this list for a couple of reasons. First and most importantly, it is our only ally in the Middle East that we could count on if the region suddenly erupted into chaos. If a new Islamic revolution swept through the area, seizing control of the oil fields and cutting off our access, what is the one country we could count on? Israel. Second, Israel has significant military power and occupies a strategic location. Third, Israel is a reliable U.S. ally because it needs us far more than we need it. Israel has few options for powerful allies. The U.S. is pretty much it. And finally, we have strong cultural ties to the country, and as with Australia in Asia, most Americans would choose to live permanently in Israel rather than any other place in the Middle East -- for obvious reasons.
5. New Zealand. I put them here for most of the same reasons as Australia, although they are smaller and less significant as an ally. That's why they are number five.
Honorable mentions: South Korea, Japan (too recent of an ally. Loses points for WW2 and before), Taiwan (loses points for being a horrible ally as mainland Nationalist China), Philippines