I've created an interactive map displaying 696 ARTCC / RCAG (Remote Center Air/Ground) transmitter locations.
The map defaults to view all centers, or you can use the pull down menu and choose just the center you're interested in.
If you click on the transmitter site a window will appear with the frequencies being used at that site. If you zoom in on the site you should be able to see the antenna farm in most cases.
You can check it out at http://www.milaircomms.com/artcc_transmitter_locations.html