I didn't like Amazon's tool, which cannot handle Web page content properly, so I wrote a new tool instead.
This tool adds
Send to Kindle context menu option to Windows Explorer for easy delivery to your Kindle device.
Additionally, it adds two context menu options to Internet Explorer:
Send to Kindle and
Save to Mobi.
Unlike other similar online tools (Bookmarklets), it does all processing locally and does not require to add any third party e-mail addresses to your approved e-mail address list.
You can send or save a highlighted selection or an entire Web page content.
There is some basic format filtering, but there is still room for improvement.
You can get it at:
http://rakar-web.appspot.com/andrej/software/
Use it freely!
Andrej