Ask HN: What do you use for HTML sanitization?

There's some established HTML sanitization solutions like HTML Purifier in PHP, but I can't seem to find their counterparts in either Java or .Net. Code samples in C# and Java are floating around, but I haven't seen anything like a project that's undergone serious testing and is being updated for new security threats on an ongoing basis.

Heck, I'd pay for a commercial component if it was well maintained. Any suggestions? Or, this being Hacker News - would someone want to create such a component as a mini-ISV startup?