Patrick, Gorings' Grenadiers is a pretty good book for unit histories of the 21 existing field divisions. However, the attributions of photos to certain units is highly suspect. In fact, many of the photos in the book came from my website. Check my site out for alot of photos. Some are definitely field division. Others, however, may just be ground troops of the Luftwaffe in other branches of service.
Actually, the best photos that I have found are in a totally unrelated book. It is called "The MP38, 40, 40/1 and 41 Submachine Gun" and its ISBN is 90-805583-2-X. I would suggest buying it for some really interesting photos.
Otherwise, there are a few Osprey books with photos: Luftwaffe Field Divisions 1941-45, ISBN 1-85532-100-9 and Luftwaffe Airborne and Field Units, ISBN 85045 114 0. The second is out of print, but you should be able to pick it up off of ebay.
That'll give you a start. Willi is also pretty darn knowledgeable on them. So, maybe he can suggest some more items.
Here's my website: 8. und 18.Feld Divisionen (Lw)