We normally charge top dollar for pictures of kittens, but today you can have these wallpapers for the low, low price of $free. They're the right resolution (aka 2560 x 1600) for your 13" MBP con Retina Display.

Affectionate Kitteh

Ambivalent Kitteh

Mac OS X Snow Kitteh

Devices from bottom to top:

13" MacBook Pro Early 2011

13" MacBook Pro Retina Late 2012

21-Day-Old Kitten Late 2012