I really want lanterns and lantern oil, personally. An upgrade to that will be LED lanterns that can be recharged with generators and other things. Lantern oil can be crafted and is easy to get, but large recharging batteries found etc.
The benefit of oil is that it lasts longer, can help start a fire, as well as easily found. But LED will be far brighter, and batteries are harder to find, but can be recharged and stored. One tin of oil lasts almost as long as 1 battery (12 in game hours for oil in small oil lantern, 14 for battery or large storage lantern)
Torches, hella easy to make and you could use them to light zombies on fire, but are very generic light sources.
Flashlights, obviously, many sizes with different batteries, as well as rechargeable batteries.
Then light bulbs that break every 12-16 ic days, etc.