Boot Animations are one of the many reasons that I love to root all of my devices. While it is just a small mod that probably only your eyes will see for just a few seconds every once in a while it is still an extra layer of personal customization that can be fun. You could always scour the web for pre made boot animations, but depending on what exactly you are working for you may not find what you are looking for, and even if you did it may not be the right size for your screen. You could always ask a developer to create the boot animation that you are looking for. You could also just build your own custom boot animations! Developer "jackeagle" has posted a tutorial on how to create your own bootanimations. You can make them out of images, or videos. Head to the link below for the full guide.
XDA