The answer to this question is of course incredibly subjective. Most people already have a favourite editor and will not be interested in changing at all.
Having said that, my own editor of choice for LaTeX work is GNU Emacs. (Note: most people will think of Emacs as a Unix editor if they think of it at all, but in fact I also use it successfully under Windows, so do not think it is your platform that is keeping you from using it.)
One of the things that makes Emacs so suitable as a LaTeX environment is the AUCTeX extension package. AUCTeX adds tons of functionality I would no longer be able to do without. It allows you to run TeX/LaTeX tools and commands right from within Emacs (using menus or keystrokes), it parses error text and can automatically position you at the point in your source file where a problem occurred, it is clever about documents split across several files, and that is just the beginning of a long list of incredibly handy features that have saved me large amounts of time.
I've been receiving some feedback about a couple of LaTeX-specific editors people have been using for their own LaTeX work, most notably Kile and LyX. I have no personal experience with these editors, but thought I'd give them a quick mention here as possible alternatives for those who have not committed themselves to an editor yet.