Novus 2 polishing compound - The only compound recommended to repair scratches and surface blemishes by the manufacturer of the clear plastic that OT uses. "For ordinary cleaning use only water, a mild solution of water and dish soap, or if needed, alcohol to clean the windows. There is a Novus 1 cleaner as well, also available online.".  This is recommend by OT. Note: this info older, it is not clear if this is safe to use on the newer scratch-resistant windshield. 

Meguiar Plast-X Clear Plastic Cleaner and Polisher - Recommended by several plastic manufacturers to preserve clear plastic finish. Kim G provided this info.

Cee Baileys Rain Repellent for Windows Highly recommended by some ELF owners though not by windshield manufacturer. Dat T provided this info.

RainX for plastics - Make sure to get the RainX for plastics. See below for standard RainX. This is recommended by Tom from OT.

Pure Carnauba Wax - This is used and recommended by several ELF owners.

NeverWet Water Repellent - Do not use - Anti-wetting treatment for many materials, but clouds up the plastic ELF window over time. This is a GREAT "undercoating" for aluminum and the side wheel wells as it keeps water based stuff from settling. It turns ANYTHING a bit milky white and is more noticable on dark higly reflective surfaces. MarkW4CHL provided this info