Four types of salt are typically used to remove ice. Sodium chloride (often called rock salt) is the most affordable, but it does the most damage to concrete and soil beneath the ice. It is useful to about 15F. Calcium chloride is effective to about -20F, but it can harm concrete and irritate your skin. While potassium chloride is only good above 20F, it won't harm your skin or plants. Meanwhile, magnesium chloride, the new salt of choice, works in temperatures as low as -15F and is the least damaging to plants. However, it will damage metal and electric utilities. None of the deicing salts will harm asphalt or wood. They are all available both online and at hardware stores; read the packages carefully to determine which type of de-icer is being sold.
Other options: Fertilizers that contain ammonium sulfate or ammonium sulfate nitrate will melt ice, but they can harm concrete and are not highly recommended. For small patches of ice, use 91% isopropyl alcohol in a spray bottle. It will loosen and melt the ice. Weird but true: Some people use a rum byproduct that smells a lot like soy sauce.
If you can forgo melting the ice and just want to improve traction, use sand, kitty litter or wood ash. Of course, you'll have to clean up the mess in the spring.
Photo credit: Aris Patelos