I know, for example, that there is an Atmospheric Correction Parameter Calculator web-tool developed by Barsi, for Single Thermal Band Instruments ( Landsat images)
You can find more informations about this tool, here:
http://atmcorr.gsfc.nasa.gov/
Other Atmospheric correction tools are incorporated in software packages, such as : ENVI ( FLAASH module), PCI Geomatica (ATMCOR), etc, etc.....
here a tutorial video:
http://www.youtube.com/watch?v=bCrWFhlq9yE