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.
Nedit is another free, programmable, editor available for Unix systems. An AUC-TeX-alike package for Nedit is available from CTAN.
Eddi4TeX (shareware) is a specially-written TeX editor which features intelligent colouring, bracket matching, syntax checking, online help and the ability to call TeX programs from within the editor. It is highly customisable, and features a powerful macro language.
You can also use GNU emacs and AUC-TeX under MSDOS.
The 4AllTeX CDROM (see TeX CDROMs) contains another powerful Windows-based shell.
Both emacs and vim are available in versions for Windows systems.
Vim is available for use on Macintosh systems.
There is another set of shell programs to help you manipulate BibTeX databases.