Amaya is a W3C's complete web browsing and authoring environment.
Bluefish is a programmer's HTML editor written using GTK, designed to save the experienced webmaster some keystrokes.
Cssed is a small developer editor and validator, that tries to ease the CSS editing.
Mozilla's Composer HTML editor keeps getting better with dynamic image and table resizing, quick insert and delete of table cells, improved CSS support, and support for positioned layers.
NVU is a WYSIWYG HTML editor with site manangement features derived from Mozilla Composer.
Quanta Plus is an HTML editor and a web development for the K Desktop Environment.

Meld is a visual diff and merge tool. You can compare two or three files and edit them in place.