jEdit's very useful Highlight Text plugin
I have to put in a good word for the jEdit text editor again. Every so often I find some astonishing new feature in it (such as search-and-run-Java-expression-on).
Here's one that comes in useful for my current i18n project: Using the jEdit Highlight Plugin (and regular expressions) to highlight code that needs to be done (white), code already done (green), and code I don't need to concern myself with (dark blue).
You can color any text you want, specifying the criteria with regular expressions.