The New York Times tonight added Mixx bookmarking buttons on its site, which is an important milestone for the company. Facebook, Digg and Yahoo Buzz are the only other third party social bookmarking services that are offered.

The NYTimes doesn’t include well known and more established services like Delicious, Reddit and others on its pages (Delicious was bumped for Mixx). And since Mixx is only six months old, so this is an important sign of confidence in the young startup.

An example is here, just click on the “share” button to the right of the article.