BILL CLINTON MathEQ (formerly known as Expressionist) is the best-of-breed mathematical typesetter, providing ease of use with exceptionally good output. I have used it for many years and have also tried (extensively) the others as they have appeared, including (especially) the free program that is commonly shipped with Word and other word processors.
For those reviewers who tout LaTeX, you should know that they are techies who love messing around with computers as opposed to getting their main work done. LaTeX is a mark-up language that does not let you even see how your program will look without going through a separate rendering stage; in the meantime, you are looking at gobbledygook expressions. With all respect to to Donald Knuth whose TeX is the basis for LaTeX, please--join the twentieth (that is, 20th) century. If you really want to use TeX or LaTeX, GraphEQ will politely export in that format. But in the meantime, you get to set your equations using common GUI techniques.
(Version 4.0.8)