For detailed information I refer to The Leica: A History Illustrating every Model and Accessory by Paul-Henry van Hasbroeck. Another good resource is Leica Manual by Willard D. Morgan and Henry M. Lester, published over many years in several editions.
" A loving and caring heart is the beginning of all knowledge " ~ Thomas Carlyle ~
A camera is a paintbrush, there are many types to accomplish different strokes. And within the Leica lineup of lenses each lens in a focal length has a different character. That said, you will ne'er be able to tell anything by looking at a computer monitor and thus all your research is for naught. The only way to understand them is to buy them and use them.
The amount of ridiculousness available on the internet is staggering and for the most part completely pointless in the pursuit of creating worthwhile images. All Leica lenses are excellent. A persons ability to use them to their full capability varies wildly. All of the actual, valuable information concerning leica lenses is contained in books written about them.
The names you asked about are simply trade names that Leica uses to describe the speed of the lenses;
Noctilux is basically an F/1 lens, there are F/1.2, F/1 and F/0.95 varieties. Noctili are completely unnecessary but I do think the out of focus areas look good. Good luck handholding at F/1 and enjoy carrying that behemoth around.
Summilux is F1.4 and makes low light color photography possible, but I say "Yuck" to low light color. Still they are useful for narrow depth of field.
Summicron is F/2 and the most practical to carry on an everyday, everywhere basis which is mostly the point of having and using the Leica. Though not all Summicrons are small.
Elmarit is F/2.8 and I believe they provide the best image qualities wide open but that's just my opinion. They are cheaper, smaller and lighter than their faster brothers and by far the easiest to carry.
Elmar is F/4 and are great lenses as well.
Your own knowledge of latin will tell you what these words actually mean.
Huge variations in price are the result of the collector markets, speeds of lenses that make them attractive to professionals who use them in low light, supply and demand, internet propaganda, Erwin Puts or whomever says the best lens is X and everyone has to have it. Leica lenses are worth the price, just as everything that is created to the highest standard is.
FWIW, I just finished an article called, "Lens Primer - The Basics" that goes into a whole lot of just that; focal length, aperture, hoods, how they're named, etc. It's written from a rather basic point of view and will be followed up by additional articles that get more advanced. This is part one, or "Lens 101."
If it has already been mentioned in the thread I apologize. I just wanted to mention http://nemeng.com/leica/. And watch out some FSU lenses have 39*1mm. threads whereas the Leica spec. is 39mm*24tpi. Slightly different but usually works. I have an Industar 61 L/D that I like in addition to my Summicron. Oh, and watch out for fakes on the auction sites http://jay.fedka.com/index_files/Page367.htm. I like my Leica better than my Fed, but it doesn't have the red hammer and sickle