O.k. Sven then for a start ...
Fw 190 D (2 vols) Japo
http://www.japo.eu/products.php?cat=3Bodenplatte John Manrho and Ron Pütz
Black Cross Red Star Bergström /Mikhailov (3 vols so far different publishers)
If you read german you can buy anything from Dr. Jochen Prien
Unit histories JG 1+11, 3, 27, 53, 77 in total 17 books and
Jagdfliegerverbände der Luftwaffe 12 vols (21 books) so far
http://www.jagdgeschwader.net/For english books have a look an Eric Mombeeks works on JG 1, 2, 4 and 5
http://www.luftwaffe.be/JG 300 (2 Vols) Jerry Crandall (I do not have his two Fw 190 dora books)
http://www.eagle-editions.com/Nachtjagd war diaries from Theo Boiten
Greenhearts - first in combat with Fw 190D by Axel Urbanke
almost everything that was published by Classic publications (and its successors). Hikoki books are also nice. Have a look at Criss Goss' "Bloody Biscay" (among others) Andrew Arthy and Morten Jessen published two books on Fw 190 usage in North Africa and MTO (more to come)
this are several thousand euros so far and I guess many of the books will be rather birtchday and x-mas presents than 2 per month (50 Euro+ books)
For a smaller start: "Luftwaffe im Focus" is a very good series and has lots of unpublished photos with good information
http://luftfahrtverlag-start.de/index.html I would not recommend Kagero or Osprey without some knowledge on the subject. Both publishers are prolific but many works on Luftwaffe subjects are not very deeply researched ... nonetheless they can be fun to read and a starter for deeper research.
If you have a special interest just ask and I try to come up with more...
all the best
Steffen