Available at: Suck UK http://www.suck.uk.com/product.php?rangeID=154&rangeNew=1 ($16)
Via: Craft http://blog.craftzine.com/archive/2010/09/invadersletterpressnotecards.html
He doesn't really look like he wants you to have a nice day, but the sentiment is there.
You always wanted to be a space ranger, this is one step closer!
I'm happy I haz you.
Available at: MimosaCards http://www.etsy.com/listing/57201344/cheeseburger-cat-im-happy-i-haz-you-set ($12 for a set of 10)