Snorkel
Scuba diving and snorkeling are very similar. The key difference in the two sports is the equipment that you use. When you snorkel you are not completely submerged in the water. You stay above the water with your face only submerged. A snorkel will allow you to breath while you are underwater. You basically attach the snorkel to the side of your mask and allow it to stay above the water. Snorkels are one piece of equipment that you can find just about anywhere. Snorkels are usually well-constructed so that you should have no problem when purchasing a used one. Although, you should ensure that the tube is in good condition and does not include any cracks.
There are essentially three types of snorkels: dry, purge, and non-purge. A dry snorkel isolates the breathing tube so that only air is allowed to enter. A purge snorkel allows both air and water in the tube, but provides an exit path for the water. A non-purge snorkel, which includes a mouthpiece with the tube is the least common type of snorkel.
You will probably be interested in either a dry or purge snorkel. The U.S. Divers ProPack includes both a dry and purging tube. This snorkel set is unique in that includes 5 pieces of equipment that you can use when you dive. The ProPack includes a high-quality mask made of silicone, a pair of scuba diving fins, a bag that you use in conjunction with the snorkel to drain water, and of course the snorkel.
The AquaLung Flex Impulse 2 Snorkel offers a purge snorkel. The features of this snorkel focus on making snorkeling more comfortable. The snorkel is designed with a more comfortable mouthpiece and has slides that enable you to easily snap the snorkel onto your mask. Most snorkels contain a two-way purge. The AquaLung has a patent on their one-way purging system. At just $23.95, this snorkel is a great deal.