Kodak D76 Negative Developer
This is the absolute classic - the most frequently purchased developer in the world. In the post-war western world, most fotojournalists developed their films in D76. In the east, people used F19, and in England the Ilford ID11. All of these developers are based on the D76 recipe from Kodak. If you ask any US photographer what "their" developer is, most will give an answer and then hang a "...or D76" on the end.
Very universal developer. Easy to use and it gives good results with all B/W films. It gives a little more contrast than the Atomal 49, but also shows more grain. Tri-X or Classicpan 200 in D76 give you "the look" of the golden era of B/W photojournalism.