BlueGriffon is a new WYSIWYG editor which uses Gecko, the Firefox 4 rendering engine for displaying the web pages. It's cross-platform and runs on Windows, Linux and Mac OSX.
What I like about it is the built-in HTML5 and CSS3 editing features - you can use it to easily apply transforms, transitions, text and box shadows, linear and radial gradients and so on. Further more, BlueGriffon comes with Google Font Directory and FontSquirrel addons so you can easily apply a custom font to your page.
You can check out all its features @ bluegriffon.org
Install BlueGriffon in Ubuntu
In my test, the latest nightly builds was more stable then the latest release (0.8) so I suggest you use that. Download the latest nightly from HERE.
Even tough there is a .deb file available for download (only for the nightlies), it's better to use the installer because the .deb is only available for 32bit and it creates the executable file in the wrong place.
Once you've downloaded the installer (its name ends with "-install"), simply right click it, select Properties > Permissions, check the "Allow executing file as program" box and then double click the downloaded file. Once installed, there should be an icon on your desktop which you can use to launch BlueGriffon.
Please note that BlueGriffon is not yet stable so expect to find bugs!
[Thanks to sourceslist.eu for mentioning BlueGriffon]