1. The Soviet Union
2. The Afghan Mujahideen
3. Saddam Hussein
I have problems with all but two entries on the list. First of all, the Soviet Union. The Soviets were our allies in WW2 purely out of necessity, and only during wartime. They were not our allies before the war, and the alliance ended with the war. I'd eliminate them from consideration.
Then there is France. France has been irritating and not a particularly good ally, but I don't think it belongs in any top 5 list of this nature. As for Saddam Hussein, I reject the notion that he was ever a U.S. ally. We favored Saddam against Iran during the Iran/Iraq War, but Iraq was a Soviet client state. What support we gave to Saddam has been greatly exaggerated.
Pakistan on the other hand should go to the top of the list. It's basically an ally in name only, and has only cooperated somewhat during the war on terror because the Bush administration put extreme pressure on it. Our relationship with Pakistan has prevented us from having closer ties with India, which, aside from being larger and more important, is actually a democratic state and should be a natural U.S. ally.
So who should be added to the list? There is one glaring absence: Saudi Arabia. How do you put France on a list of bad allies and not Saudi Arabia? Yes, they sell us oil, and help keep the price under control. That's a big plus. But you have to look at the negatives too. They are arguably the greatest sponsor of Islamic extremism in the world. And it's not like they are giving us oil for free. We helped develop their fields, help protect them, equip their military, and provide legitimacy for their backward despotic government. We have a sort of nasty symbiotic relationship with them. They are our ally purely because of oil and strategic position. They hate everything we stand for, just as many of us despise them as wealthy barbarians.
Who else? Egypt. Similar to Saudia Arabia, the Egyptians basically despise the U.S., take our money and weapons, and unlike the Saudis, provide us with nothing. Could we actually count on Egypt in any sort of crisis? Of course not. Egypt is a powder keg with strong radical Islamist elements, kept in check by a vicious dictatorship. Even more than Saudi Arabia, our alliance is with the government only. The people hate us. It could go from ally to enemy overnight, similar to what happened with Iran. And it won't be fun when all of our advanced weaponry falls into the hands of another revolutionary Islamist state.
My final nominee is Turkey. Turkey was a loyal ally throughout the Cold War, when we brought them into NATO, helped defend them against the Soviet threat, and basically supported them in every way possible, including backing their bid for EU membership. In return we got a strong ally that was more pro-Western than most Muslim states, excellent bases in a strategic location, and generally good cooperation. All that changed at the beginning of the Iraq War, when Turkey turned around and knifed the U.S. in the back, blocking us at the last minute from staging out of its territory, and massively disrupting our invasion plans. Allies you can't trust in a crisis situation aren't worth a whole lot. And we can no longer trust the Turks.
Dishonorable mentions: Mexico, Indonesia.