Stainless Steel Ball Valves 

Stainless steel ball valves are almost a necessity in homebrewing.  These are most commonly used on your kettle, allowing you to control the flow of your liquids during transfers.  Using stainless steel ball valves is recommended, as these will come in direct contact with your wort, and using anything other than stainless could leave a metalic taste in your beer.  Stainless steel ball valves are also easier to keep clean, and will last longer.