According to the Wall Street Journal real-time economics blog,

A Factiva search of the top 50 newspapers in the U.S. returns 268 stories referring to a housing or real-estate bubble in 2003. In 2004 that number increases to 369 and in 2005 it swells to 1,608. Going month by month in 2005, there’s a steady increase in “bubble” stories in the first part of the year, coming to a peak in June.

This isn’t to say that reporters somehow “got” the bubble when nobody else did. Reporters’ main job is to report, and if they’re writing more stories about a housing bubble, it’s probably because more people are saying that there is one. Indeed, 81% of respondents in an online poll in May 2005 said they thought the U.S. housing market was in a bubble. Most of the people who responded “yes” thought the bubble would keep growing.