I would like to have a comprehensive list of geographic locations in
Germany, ranked in hierarchy.

The important point is to include names that people actually use to do
searches for things like houses to buy or other locations.

So for example, in the US, this would be a list like this:

1 US
2 California (parent is 1)
3 San Fransisco (parent is 2)
4 Los Angeles (parent is 2)
5 80210 (parent is 3)
(and stop at town or postal code level- no need to go down to street level)

I would like a list like this for Germany, either point me to one
already made on the web, or create one from public sources or real
estate websites.

Ponsardin,
This is a free comment, not an "answer" to your question.

Germany has 16 federal states - "Bundesländer" (sing. Bundesland) - 
which are divided into county-like units called a "Kreis".  Some
larger cities are independent of these political entities ("Kreisfreie
Städte").  And then there are towns and smaller communities, of
course.

Here is a list of the Bundesländer where you can click to find the
Kreise and Kreisfreie Städte:
http://dmoz.org/World/Deutsch/Regional/Europa/Deutschland/Kreise_und_kreisfreie_St%c3%a4dte/

Berlin and Hamburg, as city-states are not included as they have no
"Kreise", rather "Bezirke" as shown on this map of Berlin from
Wikipedia and the excerpt on Hamburg:
http://en.wikipedia.org/wiki/Image:Berlin.png
"Hamburg is organized into seven boroughs (Bezirke) comprising 104
quarters (Stadtteile):

    * Altona
    * Bergedorf
    * Eimsbüttel
    * Harburg
    * Mitte
    * Nord
    * Wandsbek

Three small islands in the North Sea also belong to the City State of
Hamburg: Neuwerk, Scharhörn and Nigehörn."

(Bremen is also a city-state, but included in the first link.)

THis is a site that seems to have all the "Städte und Gemeinde"
(cities and smaller communities):
http://www.deutsche-staedte.de/staedte_afr.html

The black numbers are the "Postleitzahl" (PLZ = zipcode).  Of course,
larger towns have several, and private entities that receive much mail
can have their own.
This site seems to be the best one for PLZ:
http://www.postleitzahl.org/

So we have on your scheme:

Deutschland
   Bundesland
      Städte or Gemeinde
      Postleitzahl

The information about "Kreise" is superfluous for your purpose, it seems.

Please let me know if you have any questions.

Myoarin

Myoarin,

Thank you very much for your comment.

A couple of clarification questions:

- So "Kreise", or county, isn't really a category that normal people
would use to do searches for things like houses or cars for sale in an
area?
- Also, would it be common for Germans to search by "Postleitzahl
", or postalcode? I know this is very common in the UK, but never done in France

- finally, it would be interesting if you could point me to links
indicating the names of the popular zones/districts/neighborhoods for
the top 10 cities, as you started indicating for Hamburg

Why did you respond with a "comment", not an "answer"? Seems to me
you're being very helpful

Ponsardin,
Greetings,
Only G-A Researchers with blue names can post an official answer.  One
had your question locked but then did not post anything.  I am pleased
that the information in my comment is of help.

Kreise:  Yes, we do use/refer them for housing searches, but probably
only as a shorthand instead of naming the couple of towns we are
interested in, since Kreise include agricultural areas and small
villages that would be uninteresting.  Someone advertising a used car
would use the town or maybe the PLZ, which is more specific: but more
likely, the areacode for a telephone number would be adequate.  Most
people only know the area of PLZs for their own community.

Here is a free PLZ map that you can blow up to readable size.  It also
includes major areas at the bottom, but not in absolute PLZ detail.
http://www.gedcom2map.de/PLZ-Karte.pdf

If you don't mind, I will leave your final question about 10 major
areas to the researcher who had a lock on your question.  It strikes
me as being enough work to justify the price of your question.
You could help attracting him or her back to your question with a
clarification, which you can do by accessing the question again, and
repeating your request with assurance that you will accept it as an
"answer".

Glad to have been of help.
Regards, Myoarin