I use basic dawn dishwashing liquid (the $1 on that usually on the bottom self of walmart) works great, gentle on their skin and also kills fleas, they are really clean, I don't use conditioner except on my LC boy then I use Mane/tail conditioner on him. I was told by another show person to use that and I haven't used anything since except I will get one made for black dogs to help them shine alot more plus it smells great, I get that at petsmart.
I am going to show this summer but what we usually use is johnson baby don't cry shampoo. Although we usually never bath them in the winter. Have you ever noticed how hard it is to get a GSD wet? Like I have to wait for the water to get all the way through that coat! It's so weather resistant!