Night Stalker and Enchantress both have 1800 night vision. Here's a sortable complete list of Hero Stats I put together a while ago that has a list of everyone's Night Vision in Dota2. In DotA, Meepo and Slark also both have 1800 night vision.
Night Stalker is an exception in that he is the only hero who does NOT see 1800 during the day, seeing only 1200.
Enchantress is the only hero in Dota2 right now that has full vision (1800) during both the day and night. In original DotA, Meepo and Slark share this combined 3600 vision.
Luna's passive skill Lunar Blessing provides her 1800 vision range during night.