Placing a fountain in the middle of the pond and having goldfish that live in it is a great idea. One can place a liner in the pond to keep the bottom clean and keep the water from draining. By having goldfish you keep the insects down in the water and add appeal.
First you must keep in mind that the best looking back yard ponds are the ones that look most natural. chose plants that are normally found around natural ponds and lakes such as grasses and bog plants. Rocks placed randomly look good too, just make sure you bury part of them in the ground to maintian a more natural look.
When choosing plants for your pond you are going to need to keep in mind that you will need plants that do well in high moisture areas. The soil around the pond will be damp all the time and can actually kill some plants. Look for plants that thrive well in your area. You have a better chance with those.