Tels:
Actually, I just added one new link to the toolbox on the left, which goes to a HTML page with a form entry on a webserver, which bounces the user back to the wiki. I am sure it is possible to create a specialpage (Specialpages:NewArticle?) that does the same, but the external form was easier for me.
http://meta.wikimedia.org/wiki/Help:Inputbox
This has been active on the Wikimedia wikis for quite a while. I originally created it for Wikinews, but it's used in many different places now. It supports preloading text.
Erik