Agriculture Sites:

Allendale Inc.
Agriculture.com
AgWeb
CME Group 
Farmers Market Online
Farms.com
John Deere MachineFinder
Machinery Pete
ProFarmer
U.S. Department of Agriculture
WebFarmer

Agricultural Universities

Iowa State University
University of Missouri (Columbia)
University of Nebraska (Lincoln)

Extension Offices

Financial Links:

Ameritrade
CNBC
E*TRADE
Fidelity
Financial Times
Google Finance
Marketwatch
Planet Money (NPR)
The Wall Street Journal