Editors and IDEs

DoLaTeX
Latex editor with syntax highlight, document structure tree view and project handling. Latex output allows direct jump to warnings/errors, Projects folders gives support for figures/graphs. (Python, Pre-Alpha)
http://sourceforge.net/projects/dolatex

Euphoria
An editor taiored for LaTeX editing. List of features and SourceForge project page.
http://euphoria.sourceforge.net/

LaHelper - A LaTeX Command Helper
The application provides a menu system.
http://lahelper.sourceforge.net/

LaTeX
Michael Prokop describes the usage of VIM as an editor for TeX.
http://www.michael-prokop.at/computer/latex_en.html

Tcltexed
A simple text editor based on the script language Tcl/Tk, especially adapted to LaTeX written by Martin Strauß. Contains short description, downloads and screen shots.
http://tcltexed.sourceforge.net/

Texmaker
Open source multiplatform LaTeX development environment written using Qt. Features overview and download.
http://www.xm1math.net/texmaker/

Vim-LaTeX
Environment for editing LaTeX in Vim. Huge set of menus and shortcuts, improved syntax, compiler and ftplugin files, and recognition of \usepackage commands.
http://vim-latex.sourceforge.net/

Winefish
Open source LaTeX Editor written using GTK+ and based on Bluefish. Berlios project page, screenshots, forum and mailing lists.
http://winefish.berlios.de/