Take a look at the following folders:
/Library/StartupItems~/Library/StartupItems (if you have one)/Library/LaunchDaemons/Library/LaunchAgents~/Library/LaunchAgents (if you have one)
You should be able to figure out what the StartupItems do by name, but Google them if you're curious.
You can figure out exactly what the Launch Daemons and Launch Agents do by peeking inside their plist files. They'll usually contain a path to something, like a software updater.
As for removing the ones you don't want:
If you see something for a program you've deleted or uninstalled, by all means get rid of it.
If you see something for a program you do still have installed, be careful. These startup items can be as unimportant as an autoupdater or compatibility check, but it's entirely possible that the parent app needs the Item, Daemon, or Agent to run.
So, here's my advice: If you see something from an app(s) (or drivers, etc.) you do have installed, check that app's preferences to see if it lets you disable the function that requires the startup item. If it does, go ahead. If it doesn't, it's there for a reason; don't delete it.
If you really want to play with removing apps' startup stuff, do so carefully and at your own risk. Move the folder or plist to your desktop, restart, and test the app thoroughly. Even if you find it works without its startup item/agent/daemon, keep a copy so you can restore it if something goes wrong.
The following list might help you to disable some program at startup :
- Those in System Preferences » Accounts » Login Items (actually, these include the ones from 1.)
- The login hook for
loginwindow described here, read current value with defaults read com.apple.loginwindow LoginHook
- Some of those specified as part of a
launchd script (or otherwise managed by launchd). List all with sudo launchctl list. See man launchctl for details.
Regarding the launchd lists, you can see their definition files in the LaunchAgents and LaunchDaemons subdirectories of your system's Library directories:
/System/Library (you probably shouldn't touch these)/Library/ (usually for all users)/Users/yourname/Library (your own programs)
In the latter two libraries, check for anything suspicious. It's usually XML, so you can open and read them.
Best Answer
(All Users)-login items are stored in the file /Library/Preferences/com.apple.loginitems.plist. Normal user login items are saved to ~/Library/Preferences/com.apple.loginitems.plist.
Some WD apps add login or startup items to /Library/Preferences/com.apple.loginitems.plist and /Library/Preferences/loginwindow.plist.
The WD installer apps (e.g. WD Access for Mac) usually provide an uninstall feature which removes the respective app as well as login items or other installed files. The plist files itself won't get deleted though even if it was created by the WD installer.
If the uninstaller doesn't remove unwanted items you can do it yourself by either editing the global plist file or removing the complete plist.
A default file /Library/Preferences/com.apple.loginitems.plist or ../loginwindow.plist doesn't exist (in Sierra) but may have been created and modified by other installers. You can get the content by executing
sudo defaults read /path/to/plistin the Terminal.app window.