Here is a funny website I recently came across that is similar to the web-postcard site, someecards.com.  Here are some samples from dearblankpleaseblank.com

Dear Santa,

Quit acting like you're the one who started Christmas.

Sincerely, Jesus.

***

Dear Math Students,

Well maybe I hate you too...

Sincerely, Math.

***

Dear Tooth Fairy,

Thank you for teaching me that it's okay to sell my body for money.

Sincerely, little girls around the world.