This is interesting. The Daily Kos looked at where their stories originated (both primary and secondary sources), and found that newspapers were the main most common source. Not very surprising given the type of blog The Daily Kos is, but still.

Newspapers: 102 primary, 21 secondary
Blogs: 83 primary, 19 secondary
Advocacy organizations: 77 primary, 9 secondary
Television network: 69 primary, 14 secondary
Online news organizations: 54 primary, 5 secondary
Magazines and journals: 36 primary
Political trade press: 28 primary
Research/polling: 20 primary
Wikipedia: 21 primary, 8 secondary
Educational (.edu): 15 primary
Government: 14 primary, 5 secondary
Campaigns: 13 primary
Books: 6 primary
AP and other Wire: 5 secondary
Radio: 4 primary

Read the full thing, with something of an analysis, and take to heart if you will.