I'll attempt to give some best-in-show running commentary to make this a little more interesting.

Splash Screen

I've gone for the black theme here with a total eclipse graphical representation, representing well... an eclipse. Pretty heavy stuff in my humble opinion or should I say imho. You'll notice the loading text straying a little towards the border and this is purely because I can't change this. Period.

Icon set

Again keeping with the black theme I couldn't resist using a visual representation of what a programmer might feel when using this superb IDE... Yes I know it's another Eclipse but that is part of the theme.

Install

Pretty easy. Just do a wildcard search for "eclipse*" on your eclipse installtion folder and replace the images with the same name. If you are worried this might break anything just rename your existing images to something other than what they are currently called. You could use the plugin Random Splash Screen if you just want to change the splash screen and require a GUI to do so.

Download the zip file here »

Selah.

[Update: Someone asked about Flex/Flash Builder: Just change your wildcard search to flexbuilder* and all the icons should appear. There does seem to be .ico files being used - so for those you will have to convert one of the PNG's using some program to .ico]