You can have different water pond designs, however ones that don't restrict water movement are the best. What I mean by that is you don't want to have a backyard pond with tight corners in it where it will be hard for water to circulate.
The best water pond designs are round, oblong, or kidney shape. They look the nicest when finished off with lots of different flowers and plants around them. They seem to look more natural than say a square one. I'm sure there are plenty of nice looking square ones though.
Everyone has their own tastes on what they like and what they don't. I highly suggest that you have a waterfall for your pond. The sound of the water rushing over the rocks is very relaxing and it looks great, it also helps aerate the water for the fish.
Flat pieces of sandstone stacked around the pond give it a very natural look and is very popular as far as water pond designs go. Other things that can be used are fieldstone, pebbles, bricks, mulch, or any combination thereof. Just use your imagination.
When you are designing your pond, please keep in mind that if you are going to have pumps and filters, you're going to need an electrical supply nearby and don't forget some kind of water supply.
Your best bet is to search around the Internet and look at different pond pictures and decide what you want to go with, there's a lot of information out there to be had. I hope this helps a little with your question about water pond designs.
Robert Dorrance has had a pond for the last eight years and would like to share his experiences with you. Be sure to come by and download the free e-book, How To Build A Beautiful Backyard Pond. Find out more at http://www.Backyard-Pond-Guide.com