Learn to live with it: Every application that customizes the context menu does so in its own way. In some cases you may need to hunt through dialog boxes, scour the application's help file, or scan the vendor's Web site to find out how to remove context-menu entries. In other cases you have to accept that some context menu commands are there to stay.
For example, though you can use the Registry editing tip above to remove the 'Scan for Viruses' command added by McAfee VirusScan, I have encountered no way to remove the context-menu commands added by Norton AntiVirus. Your only option in these cases is to live with the extra clutter and to contact the software manufacturer to voice your opinion on this subject.