In "The Pilot", Chandler and Joey helped Ross to assemble his new furniture. It appeared in the series less than his third apartment, but there have been shown memorable moments, like when they play poker in a first season episode.
When Rachel asks Ross to take a break from each other, and he sleeps with a girl who works on a Xerox Store, it takes place in this apartment.
In Season Four, Ross proposes to Emily in that place. In Season Five, after marrying Emily he moved into a new apartment that he was renting from Emily's cousin, because she didn't want to live in a apartment that had things that Rachel has touched.