often the installation dmg has an uninstall applet.
failing that, trash the application and then go looking in Library/Application Support
and ~/Library/Application Support
if you find any likely offenders but are not CERTAIN that they are related, move the folder somewhere else from which it can be restored. if you are certain then trash the folder.
however as twiSSt points out, the software author usually publishes uninstall info on its website and that should be your first port of call if you no longer have the dmg with uninstall script.