I'm interested in some "general" essays on something which can be named "philosophy", but is not limited by "pure thought".
I think that good essayist creates new "general" concepts and explains them with his wide knowledge. If his ideas illustrated by biological examples, they are not limited by biology.
If an essayist is great and his ideas are great, then his choice of science or area of knowledge is not really necessary be one of my favourites. (Again, that is my own opinion)
So I'd like to read about history, politics, molecular biology, programming on LISP language, literature, music, sociology, theory of chaos, magnetic fields and such - if ideas are good, they are applicable to my life and work, whatever I do; and if an area of knowledge is new to me, then I'll be more educated person then I was before reading essay. And that's what I value.