Many aquarists prefer the convenience of Hang-On-Tank equipment. If you have the room (usually less than 8") on either the back or sides of your aquarium, you will find this a great place to hang all of your new tank toys. Almost every type of saltwater aquarium equipment can be found in a Hang-On-Tank style. The following links will give you an idea of what Hang-On-Tank equipment is available on the market and how much the prices vary.
You can easily mix & match different pieces to complete your fitration system design.
If you have any questions, the Forums is a good place to post them or to see if someone else had the same question, which has already been answered.