Startup Control Panel
It lists all of the programs that are set to start when Windows does and allows you to decide what gets to start up with Windows and what doesn't. It's available as both a Control Panel applet or as a standalone program and it's simple to use. Don't want a program to start up with Windows? Just right click on it in Startup Control Panel and select disable. If you later decide you want the program to run, just re-enable it or select Run Now and it will launch.