This is a great site! It tells you about some of the most common breeds, very rare breeds, and even some mutts. It also has a breed selector here. Every time I take this particular selector it always tells me to get a ainu dog.

My favourite breeds are the catahoula leopard dog and the German shepherd dog. However, I don't know if they'd be right for you. They both have alot of energy (mainly the cata) and they both need to be physically and mentally stimulated day in and day out. You can find their pictures and descriptions of the site I gave you.