Texmaker

Texmaker is a cross-platform open source LaTeX editor.

[edit] Features

a unicode editor to write LaTeX source files (syntax highlighting, undo-redo, search-replace, spell checker...)
the principal LaTex tags can be inserted directly with the "LaTeX" and "Math" menus
370 mathematical symbols can be inserted in just one click
wizards to generate code ('Quick document', 'Quick letter', tabular, tabbing and array environments)
LaTeX-related programs can be launched via the "Tools" menu
the standard Bibtex entry types can be inserted in the ".bib" file with the "Bibliography" menu
a "structure view" of the document for easier navigation of a document (by clicking on an item in the "Structure" frame, you can jump directly to the corresponding part of your document
extensive LaTeX documentation
in the "Messages / Log File" frame, one can see information about processes and the logfile after a LaTeX compilation
the "Next Latex Error" and "Previous Latex Error" commands let you reach the LaTeX errors detected in the log file
by clicking on the number of a line in the log file, the cursor jumps to the corresponding line in the editor
an integrated LaTeX to html conversion tool