Gretchen

Too bad the English pronunciation isn't very nice, it does sound very lovely if you say it in German.
I don't agree that it sounds like "GRET-khen" though (and certainly not Gretken!). Yes it is difficult to describe the -chen sound because it does not exist in English - but I will try!
The first part sounds kind of like the English word Gray.
The second part as if you said "tee-yen" very quickly. (You know how the English word Queen is made out of the sound kə-ween? You say it just that fast.)
So altogether it sounds kind of like GRAY-teeyen.
Sorry if this was confusing. You might be better off just going to the link that was posted above.
Hope it helped! Please correct me if I am wrong. My mother speaks German and lived in North-West Germany so the accent might be different.

German pronunciation is "grechen".

Listen to the German pronunciation of Gretchen here:
http://www.nordicnames.de/Aussprache.html.

German pronunciation: GREHT-khen (note: 'kh' is not the exact pronunciation here but it is the closest you can get to the German 'ch') [noted -ed]
This name is not very popular in Germany today. It is still known to people through Goethe's 'Faust' but it is considered old fashioned.