Program: Blue Griffon
License: Open Source
Use: Blue Griffon is a web editor, it is based on the same rendering engine as Firefox/Thunderbird/Most other Mozilla apps.
Other: Not sure weather or not it leaves registry files, and all that stuff. Does not have a formal installer, you just un-extract the .zip archive and click on the icon.
Blue Griffon is a great HTML editor, and it would be a great idea for someone to make this portable.