Do check out shelters and breed rescues. A 6-month-old dog of any breed is still a puppy, but is past that roly-poly stage and so less "adoptable." German Shepherds are great, but prepare to enroll in an obedience course with him or her, and do a lot of training. They are very smart (in general) and quick to learn, but also quick to test your limits, or get bored, which leads to "bad dog" behavior. Read a good dog training book, and be very sure of yourself, and prepare to be really consistent - doggedly so. As this is your first pup, the more you know beforehand the better!

Consider the following factors:
What size dog do you generally like?
How much grooming do you want to do? Are you willing to take a dog to a groomer regularly?
How many hours per day would the dog be home alone?
Are there parks nearby where the dog could get exercise?
Do "barky" dogs annoy you?
How much time are you willing to spend training a dog?

It doesn't hurt to choose a few breeds whose characteristics you particularly like, and then go on petfinder.org or to your local shelters or both ...