Is the edit control I\'m typing in now, with all its buttons and rules freely available for use?
My web project is also .Net based.
The WMD editor is completely free (in the speech and beer senses of the word). It's available under an MIT-style license.
It's the WMD Markdown editor which is free and seems to be pretty easy to use. Just include the javascript for it and (in the easiest case), it just attaches to the first textarea it finds.
Here's some info about the Perl implementation of Markdown which, according to the site, WMD is 100% compatible with.
@Chris Upchurch Technically the current release isn't open-source, just free to use. The next version is supposed to be released with an MIT license though.
"now completely free to use. The next release will be open source under an MIT-style license."
I don't know about this control, but TinyMCE is:
http://tinymce.moxiecode.com/
It's what wordpress etc use.