How to show a list of processes that are launched upon a login?
launchd and the Login Items pane of Accounts preferences are the two places that normally start a process when you log in.

If you don't see the item in System Preferences -> Accounts -> specific account ->  Login Items then you will have to look into launchd.

Basically the LaunchAgents and LaunchDaemons folders in ~/Library

Lastly, if they are not there, then it's a system level launchd task that you might want to use launchctl to show or look in /Library instead of the user level library.

Most people just have to manage the preference pane. Here is a snap of mine showing the Activity Monitor selected and ready to be deleted if I press the – button.