Update 2018 TL;DR; LaTEX for WPF https://github.com/ForNeVeR/wpf-math
Original question I need to have a way to draw a mathematical formula in Windows Forms or WPF. Some "FormulaTextBox" control would be exactly what I need.
I'm not asking about full implementation of LaTEX, but at least something beyond RichTextBox possibilities, with division lines, square roots, etc.
Here's a list of options, pulled from several webpages online, as well as a few similar questions on SO
tex4ht
package renders math equations to imagesWebBrowser
control, and just locally include one of many javascript libraries for rendering LaTex.