You'd be surprised. Off the top of my head, Stephanie Sheh, Tiffany Grant, Dan Green, Steve Staley, Cindy Robinson, and Carrie Kerranen have moaned on camera. It's weird to see, I dunno, Orihime from Bleach talking normally, then the next thing you know she's fellating a banana.
Those are mostly LA VAs. I don't know if any of the older Texas VAs have done the porn, but some newer voices have. Uh, Amber Lee Connors (who has a Doxemon entry here for whatever reason), Sarah Wiedenheft (ditto), Natalie Hoover, Matt Shipman, and Brittany Lauda.