I'm not sure if this link was posted before, but I just stumbled upon it the other day quite by accident. It's quite an interesting study of "bad" postcards ("bad" meaning a poor choice of subject matter).
One word of warning: The site is quite addictive and goes for many, many dozens of pages, so you can spend (waste) a lot of time looking at the material, but it can be fun nonetheless!
http://bad-postcards.tumblr.com/page/2