Emacs
AUCTeX mode for LaTeX
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).
ESS mode for R
Emacs Speaks Statistics (ESS) is an add-on package for emacs-based text editors such as GNU Emacs and XEmacs. It is designed to support editing of scripts and interaction with various statistical analysis programs such S-Plus, R, SAS, Stata, and others. Although all users of these statistical analysis programs are welcome to apply ESS, advanced users or professionals who regularly work with text-based statistical analysis scripts, with various statistical languages/programs, or with different operating systems might benefit from it the most.