Easter Eggs and Secret Rooms

[drex]

I have played all through this series and I confess I have a bad habit. Regardless of the game's replay value, I find that I rarely replay a game after the first time.

So, to encourage playing a second time around, I was wondering if anyone has found any secret rooms/easter eggs hidden in the game. If you know of any post them here! Put them in the Spoiler format so that we don't give away to much if someone stumbles upon this.

Secrets I already know:

Spoiler below!

The Schmup.exe file and the password for it.
The Super Secret file and the password for it.