Eject any disc even if system cannot boot

In the newest versions of the boot manager (Intel only, I believe), it is possible to simply Option-Boot the computer and press the Eject key on the keyboard to eject a disc. This works even if your computer has a completely blank, newly-formatted hard drive.

This may also work on the older PowerPC versions of the boot manager, but I haven't tested it.

You could also press and hold the left Mouse or Trackpad button when starting your computer. Any CD/DVD will then eject.