Recent CTAN additions: dynkin-diagrams, rank-2-roots
I just ran into 2 very interesting new LaTeX packages:
Both are by Ben McKay, and make writing something involving root systems or Dynkin diagrams much easier. The first package allows one to systematically draw all kinds of variations on Dynkin diagrams using a very powerful syntax, whilst the other makes drawing rank 2 root diagrams a walk in the park. I strongly suggest you take a look at the examples in the documentation.
I might turn this into an irregular series of new CTAN addition highlights. Who knows.