There are good TeX-writing environments and editors for most operating systems; some are described below, but this is only a personal selection:
Many who fail to find the versions of emacs attractive, prefer vim, a highly configurable editor (also available for Windows and Macintosh systems). Many plugins are available to support the needs of the (La)TeX user, including syntax highlighting, calling TeX programs, auto-insertion and -completion of common (La)TeX structures, and browsing LaTeX help. The scripts auctex.vim and bibtex.vim seem to be the most common recommendations.
The editor NEdit is also free and programmable, and is available for Unix systems. An AUC-TeX-alike set of extensions for NEdit is available from CTAN.
LaTeX4Jed provides much enhanced LaTeX support for the jed editor. LaTeX4Jed is similar to AUC-TeX: menus, shortcuts, templates, syntax highlighting, document outline, integrated debugging, symbol completion, full integration with external programs, and more. It was designed with both the beginner and the advanced LaTeX user in mind.
The Kile editor that is provided with the KDE window manager provides GUI "shell-like" facilities, in a similar way to the the widely-praised Winedt (see below); details (and downloads) are available from the project's home on SourceForge. A newer system (by Kile's original author), texmaker doesn't rely on KDE's facilities, and so may be more easily portable.
You can also use GNU emacs and AUC-TeX under MSDOS.
Winedt, a shareware package, is also highly spoken of. It too provides a shell for the use of TeX and related programs, as well as a powerful and well-configured editor.
Both emacs and vim are available in versions for Windows systems.
For MacOS X users, the tool of choice appears to be TeXShop, which combines an editor and a shell with a coherent philosophy of dealing with (La)TeX in the OS X environment.
Vim is available for use on Macintosh systems.
While many (La)TeX-oriented editors can support work on BibTeX files, there are many systems that provide specific "database-like" access to your BibTeX files - see "creating a bibliography file".
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=editors