I can't count the number of projects where the user's have asked for a text-input area "just like Microsoft Word". Inevitably they also ask for some specific feature or function that means the last control I used is not quite right.
Here is a list (for future reference) of some of the open source alternatives: Open Source WYSIWYG Through-The-Web Editors.
Of course, there's always RichTextBox if you want to pay (and get support!).
p.s. blogging has slowed dramatically in this new job. Hopefully it'll be more regular in the new year!