AUCTeX

AUCTeX is an extensible package for writing and formatting TeX files in GNU Emacs and XEmacs. It supports many different TeX macro packages, including AMS-TeX, LaTeX, Texinfo, ConTeXt, and docTeX (dtx files). AUCTeX includes preview-latex which makes LaTeX a tightly integrated component of your editing WorkFlow by visualizing selected source chunks (such as single formulas or graphics) directly as images in the source buffer.