Watch The Shawshank Redemption.
Go to the local humane shelter and play with some homeless animals. Not advisable if you don't want to end up going home with a new pet, however.

Funny stuff on YouTube tends to make me smile.
Nick Cage Losing it: http://www.youtube.com/watch?v=xP1-oquwoL8
NOOOOOO compilation: http://www.youtube.com/watch?v=Eal4fep7pK4
Squirrels on twirl bird feeders: http://www.youtube.com/watch?v=pTDldZN20R0
...your mileage may vary.