Download the script (see Rob's note below) into a text file, save it as /bin/nss, or somewhere else in your path. Open the Terminal and type chmod +x /bin/nss, and then rehash. Now you can start the program by just typing nss.
one last note: if you move a modified app out of the folders that are watched for (NS) services apps = those that are checked by the script to generate the app-list, then you can't reenable the services anymore because the script does not find the app. just move the app somewhere in the searched folders and regenerate the app-list. the searched folders are: /Applications, /Library, /System/Library, ~/Applications, and ~/Library.
[robg adds: This script appeared as a comment to an older hint about removing items from the services menu, but I felt this was a unique-enough solution that it merited publishing on its own. Due to the length of the script, I uploaded it to macosxhints as a separate Stuffed text file -- nss.sit [2kb]. Expand the archive and follow the directions in the "Download the script..." paragraph above.
When you first run the script, you'll be asked to authenticate, and then it searches for all installed apps, then digs out those with services. At that point, you can choose to skip the core services from the next step (ie you'll never want to disable the core services), and then you're offered the chance to enable or disable each application's services one at a time. Overall, this is a much nicer solution than hand-editing plist files ... now, if someone would just wrap it in a GUI :)...]

