A couple of freebies
There are a lot of free text editors available online (my favorite is NoteTab Light) but most of them are designed for programmers, not writers.
One exception is RoughDraft, Richard Salsbury's clever and useful word processor made with creative writing in mind. All the confusing MS-Word-like features are missing (mail-merge much lately?), and in their place RD provides formatting features for writing fiction, poetry, stage plays and screenplays. RD also handles regular old RTF files. It used to be donation-ware, but with the release of the new version 3.0 he has made it officially freeware. More people should know about this nice piece of work.
Between RoughDraft and NoteTab, most people's editing needs are covered, and they're both lightweight enough to work on just about any Windows computer.