Links on Liberation of Cologne
The Kölner Stadt-Anzeiger has a number of articles on the liberation, the best one dealing with the mobilization of children for civil defense (Googl-English).
Lambertin has a comprehesive archive of photographs of the destruction and daily life in the first year (the gallery starts here). Some of the famous photographs of Hermann Claasen are here.
On a slightly unrelated note, NS-Dokumentation has a presentation on the songs of the Edelweiss Pirates, a gang that formed in opposition to the conformity of the Hitler Youth. Contemporary recordings of the songs can be hear at the left (check out this one, "Es was in Shanghai (Once in Shanghai)", a tramp song by Jean Juelich).