Windows only: We won't judge you by your startup sound or music, but your co-workers might. Keep your startup silent and embarrassment-free with system tray utility Auto Mute, which runs in the background and mutes your sound on logoff, suspend and shutdown.
You sound will stay muted until you manually un-mute it, which can be done easily through a simple shortcut decided by you. This way, not only will your startup be quiet, but your entire session will be quiet unless you say otherwise — especially nice if you are working in public and don't want unintended noises exploding from your laptop.
What's even nicer about this program is that it's portable — no need to install, even though it can run at startup and in the background. Just extract it wherever you want and you're done. It's also fairly low on system resources, which is always something we like to see, especially if we're about to give it "launch on startup" privileges.
Auto Mute is a free download, Windows only.