I know this is an old thread, but since I see some recent posts in here, figured I throw this in to help. Not sure why this information isn't more readily available online but instead just talk about login items. Also don't know why apple doesn't provide a prefpane to manage them.
There are 3 places to look for startup apps like you're talking about.
/Library/LaunchAgents
<user>/Library/LaunchAgents
/Library/LaunchDaemons
Remove the *.plist files for any apps that you don't want to auto-start.
I highly recommend backing up these folders before deleting anything out of them. There are several apps that require a background process and removing it from here will prevent that app from functioning correctly.
You will also notice some other LaunchAgents and LaunchDaemons folders out there if you search for them in Finder. I'd recommend not messing with any of those. As far as I've ever noticed those are all Apple internal stuff.