Dynamic Lights - very useful resource with shaders. It introduces a brand new application of the usual torches. Now, when You take in hand a burning stick, all around immediately illuminated with bright light, and You will be easier to explore the dark corners of caves and dungeons. And yet, going into adventure impenetrable night, it will be easier to look for the approaching monsters. With the addon You will surely save more coal and wood for other useful things, such as cooking or construction.
This is a useful package of shaders, which shows thin red lines the boundaries of chunks. The entire game world is divided into many pieces and now You don't have to guess where a particular chunk is located. Shaders will help to calculate the length and width of something, and to unravel the mysteries of many seeds with interesting generations, as the chunks will be clearly seen where one or the other structure.