Source: Hitching a ride. - Funny Pictures
Stashed in: Lolcats!, gifs, Goats!
YouTube videos of cats riding things.
A Tumblr search of "cats riding things" reveals... only a video version of your gif.
Luckily, Memetastic has Paula Deen riding a cat:
Tiny Cat Trap gif
Kitten action sequence with explosions gif
Hummingbird Hand Fed Eating Nectar gif
Most Subtle gif Ever