The bootup one displays very cool. Looks like it was made for the unit hehe.
Here is a preview of the main image I use...
Bootup-Starts a all white screen, then floods with the blue to reveal the apple outline in white!
Shutdown-starts with the all blue and white apple logo, then the background fades to black.
The animation shows up very smoothly...give me feedback if you try these.
Can download the zip of the bootup/shutdown via the link below
Rocker81's Bootup+Shutdown Animations