A good text editor is a real nitty-gritty tool for any localizer. I know that many of you use UltraEdit, but there are excellent open source solutions around as well. From my daily experience I can recommend two of them:
This editor is written in C++ (hence the name) and based on Scintilla. It is fairly fast, has good syntax highlighting, and a mutlti tab view that allows examining documents side by side. It is really i18n friendly and supports conversion/view of the most common codepages (including a useful rtl/ltr switcher).
There are many additional plugins (e.g. an hex editor or a simple diff tool) available from the project page; one of my favourites is NPPExport that allows saving (highlighted) text as HTML or RTF. If you ever have tried to save a simple plain text to RTF with Word you’ll be grateful for the simple RTF produced by the plugin 🙂
Even though the regex support is somewhat limited (\n cannot be used) Notepad++ definitely is my bread-and-butter editor.
As the name suggests, jEdit is an editor completely written in Java. Maybe it starts a little slower than other tools, but that is negligible. jEdit comes with syntax highlighting for a wealth of different file types, and has (due to its Java nature) a real excellent support for encodings and regex. It is fully scriptable (using Beanshell or Python), and there are tons of plugins and ready-made macros available from the project site.
As a matter of fact: there is almost nothing you cannot do with a text file in jEdit.