Many a times, the Windows Control Panel, Uninstall Programs applet proves insufficient for un-installing AntiVirus or Security Suite installations, as a result of which they leave unwanted remnants on your PC. This often then causes problems esp when you go on to install another security program. Its thus always advisable to use the AntiVirus Removal Tools or AntiVirus Uninstallers for completely removing anti-virus software.
AntiVirus Removal Tools
Here is a list of for leading antivirus and security software for Windows.
Avast : Use their uninstallation utility AvastClear.
AVG : AVG Uninstaller.
Avira : Avira AntiVir Registry Cleaner Tool will help you clean up all the registry entries left by this anti-virus software after the uninstallation.
CA Internet Security : Knowledge document and uninstaller.
Dr.Web : Removal Tool.
F-Secure : Un-installation support and tool.
G DATA : Download and use the G Data removal tool AVKCleaner. See under the Tools tab here.
Kaspersky : They offer a free utility that helps you to completely remove all Kaspersky Labs products. Download Kaspersky Products Remover.
McAfee : The McAfee Consumer Product Removal tool (MCPR.exe) removes all 2005, 2006, 2007, 2008, 2009, etc, versions of McAfee products. This option should be used, only after you remove your McAfee product through Uninstall Programs.
Malwarebytes: MBAM Cleaner.
Microsoft Security Essentials: This Fix It helps you uninstall Microsoft Security Essentials.
NOD32 : To remove NOD32 antivirus from your Windows, simply click on the NOD32 Removal Tool, click Yes, & wait for the removal confirmation.
Panda : Panda Uninstaller.
Quick Heal : Uninstaller.
Symantec (Norton) : Use Norton Removal Tool.
Vipre AntiVirus : VP Cleaner.
ZoneAlarm: ZoneAlarm Uninstallers.
If I am missing something, please add a comment below.