Chris Gibbons started Economic Gardening in Littleton, CO.  The site there gives you an historic overview.  You can also see the yearly reports that they have to the city council and the services they provide.
Littleton, CO, site with Economic Gardening Introduction

The Edward Lowe Foundation has offered key support for Economic Gardening.  In particular, they sponsor state-wide "Companies to Watch" competitions which target "Stage 2" companies with between 10 and 100 employees who are growing.  These companies are considered the best source for growing new jobs.
Edward Lowe Foundation

Wyoming has a state-wide program to provide competitive intelligence to Wyoming businesses.  They have centralized this research function for efficiency.  Here's a powerpoint on their approach.
Wyoming Economic Gardening Powerpoint

Florida has a very active state-wide program centered around the University of Central Florida.  Here's a link to their first year report and economic impact survey, which seems more realistic than most of the economic impact surveys I see. (LMegill editorial comment)
Florida Economic Gardening Program

For a more dispassionate analysis of Economic Gardening, the Federal Reserve Bank of Atlanta has a clear summary and description of the program in Georgia.
Fed Reserve Report on Economic Gardening

Christine Hamilton-Pennell worked under Chris Gibbons in Littleton and now is on her own and has an excellent set of articles and resources:
Economic Gardening Resource List
Economic Gardening Tips by Christine Hamilton-Pennell