Obama and Dick Cheney agree that it was OK to kill Anwar al-Awlaki with a drone attack. Dennis Kucinich, about as far away on the political spectrum as possible, both thing it was wrong and illegal. Heck, Ron Paul is talking about impeaching Obama over the incident.
This certainly makes for interesting reading. And it's always a little amusing to see people who normally disagree, link up on a topic. What it doesn't do, however, is help you understand the actual nuances of the case in question.
I did some poking around, and did find some useful resources. I share them here in the spirit of treating this issue like it should be: a complex one that needs to be understood from a multitude of angles.
First off, here's the transcript of a speech given by Harold Koh, a lawyer for the Obama administration. He gave it back in March of 2010, and specifically addresses some of the legal issues behind drone based targeted killings. Agree with it or not, at least it's spelled out. Here's a Rise of The Drones II: Examining the Legality of Unmanned Targeting to be surprisingly riveting (transcript is here). It was held back in April of 2010, and they specifically discuss the possibility of targeting Anwar al-Awlaki with a drone. The experts on the panel show just how divided the legal pros are on this. Some see no problem with the administration's strategy, as outlined by Koh, others see it as obviously flawed. I'm still making my way through the all the videos of the hearings, but the topic of citizenship was brought up and there seems to be some agreement that it's not the issue which the legality of drone attacks pivots on. In other words, if you believe it's OK to use drones in this type of context, the fact that the person you're targeting is an American citizen isn't really a roadblock. On the other hand, if you think that it's not a valid use of force, then the fact that the target is American or not isn't really relevant.
The hearings are on YouTube and I'll embed them below. Definitely worth a watch.