<p>If possible one that supports at least spell checking:</p>

<ul>
<li>C# string literals</li>
<li>HTML content</li>
<li>Comments</li>
</ul>

FxCop ships with a spell check now
- have you tried that?
Here's a nice add-on
for Visual Studio 2005/2008 by Mikhail Arkhipov of MSFT.