The "
Progressive Caucus" consists of Democratic Congresspersons who consider themselves progressives, such as Ed Markey.
Progressive Democrats of America is a group for Democratic activists who want to elect more progressives elected to Congress.
This article at the PDA website may be what you're looking for:
http://www.pdamerica.org/articles/news/2006-11-10-08-07-52-news.php"Progressives Increase Their Numbers as Largest Group Within the House Democratic Caucus
November 10, 2006, Washington, DC
PDA National Board Members Rep Barbara Lee and Lynn Woolsey, Co-Chairs of the Congressional Progressive Caucus (CPC), anticipate adding at least seven new CPC Members in the 110th Congress. This would increase the size of the CPC to at least 71 Members, making it by far the largest and most diverse sub-group among all Democrats in the new 110th Congress to take office in January and an increase of 14 new House Members in just the past 18 months."