Okay lets see we left off at 3 SOOOOO
4 year anniversary- A house! by now you should be married long enough that living in something rented is driving you nuts, you need your own space so yeah a house is a great gift.
5th - It is time for more jewelry, gemstones are a good choice at this point. rubies, emeralds, sapphires, opals, amethyst are all good choices.
6th- You have made it past the first real milestone in your marriage good for you! Buy your love something BIG for her favorite hobby, is she a scrapbooker buy her a nice SLR camera, does she quilt I think a new machine is in order, Maybe she likes to garden (UGG I can't imagine that but ok) buy her a roto-tiller (okay I am reaching with that one cause I have no idea what you would want if you gardened)Or maybe build her a gazebo to appreciate her garden from.
okay off to continue my running around but rest assured I wont leave you hanging on your gift buying I will be back.