The usual guidelines for potting a Bonsai.... the depth should be equal to the diameter of the trunk, and about as wide as 2/3's the trees canopy spread and or height. Oval pots are generally used for more sleek streamline, feminine trees while rectangular pots are used for a tree with masculine qualities. Japanese Tokoname are generally considered the best quality. You can purchase good quality handmade pots off many bonsai websites as well as eBay, but keep in mind the high quality pots dont come cheap. Sara Rayner is also the top US pot producer.

If you are still new to the hobby I recommend reading as many bonsai books as possibly, your local library should have a decent selection John Naka's book is also a great highly recommended book. Finding your local bonsai club is the best bet as you can talk with its members who would be more than willing to give you any help you need as well as give you the in and outs of working with a multitude of species in your exact geographical location.

-Mike