Here are some websites that you might find of interest. The first has descriptive material on all the symphonic works. http://w3.rz-berlin.mpg.de/cmp/mahler_symphonies.html The second is a more general collection of very interesting material. http://www.mahlerarchives.net/ The last is again an interpretation of his large form works. http://www.musicweb-international.com/Mahler/index.html I encourage you to search Google for more entries that you like. If you find some, post them her for the benefit of the rest of us.