Or you could get the Black Light screen saver (don't know where, you could try a few different places including <a href="http://www.apple.com/macosx)." target="_blank">www.apple.com/macosx).</a> You can set it to only invert the screen. That's kinda fun.
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I like the grey one very much. makes OS X look like it was from the 50thies.