It's hard for me, my Win 7 changes mine every 10 minutes. I have it set for pics of my 18 month old (going back to when she was born). Here's a recent one that she didn't know it was on her nose.
I thought this was freakin' hilarious... Yep, its James Hetfield, the lead singer from Metallica, I hate this song, and most new Metallica actually... But this face is priceless.