James M at Grognardia has been running a series of posts about Rangers here and here.
Rangers are a powerful image from Tolkien's stories that often makes the leap into other people's fantasy campaigns. Probably one reason that the Rangers are one of the few cool things that humans get to be in the Lord of the Rings. Another is that various portrayals of Aragorn are so damn cool including the one from the fan made Hunt for Gollum.
Elves are not Rangers because the Tolkien Rangers are the Dunedain the descendants of the Numenorians of Arnor. Their bag of features/skills are products of a specific culture at a specific time.
This is the heart of the problem Rangers have with various D&D editions. The core D&D classes are designed to be of general use. I think any campaign would be enriched by cultural specific classes but would not be good in a core rulebook.
The OD&D and AD&D ranger really don't make sense without the context of Tolkien. Shorn of its root, the Ranger is a class in search of a home. The evolution in recent editions have been to turn the class into a generalized hunter, or a fighter that specialized in two blade fighting styles. All of which should have been made fighter options if you are going down the feat, power and skill route.
The interpretation of the Ranger I liked the best is the one I created. I know that sounds conceited but hear me out. Like Gygax and other authors, I faced the problem how to work them in to a setting that lacked the context of Lord of the Rings.
One of the cool things about Tolkien's rangers is that they helped a lot of people without them knowing. Mainly by guarding their borders and hunting down evil or monsters that threatened them. Rather than re-imagine them as hunters or specialist fighters, I instead focused on this aspect.
I always felt that D&D's stable of demi-humans was portrayed as very cosmopolitan. Multi-racial adventuring parties were common. True that the rules had an animosity between the dwarves and elves. But in practice games were a mixed bag of races.
I combined the two to create my version of the Rangers. It is a pan-racial group of people dedicated to defending all of the good-aligned races against the monsters encroaching from the wilderness. Their specific approach is to go into the wilderness and deal with the problem before they emerge.
I feel this interpretation ties together the desperate powers of the original Ranger in a nice package. It is also generic enough to be useful in any fantasy campaign that has multiple races running around and adventuring together. How together or influential this organization it up to the referee but I feel it would be applicable to just about any fantasy campaign based on D&D.