You hardcore Trekkers may already know this, but I didn't: Brent Spiner, the actor who played Lt. Data on Star Trek: TNG does a spot-on impression of Patrick Stewart. I stumbled across this video at the Mary Sue and it floored me. I didn't even know Spiner did impressions at all! But doing a search revealed that Spiner's done this impression many times for fans. Still, I don't think it will ever get old.
[Via Mary Sue]