Bilateral filter is usually the effect behind those "make your photo into a cartoon" websites. 

It's an edge preserving noise removal filter.  Check out its wiki.

This is a filter found in the Noise category. Unlike many other filters in that category, this one doesn't add noise. It removes it.




At first look, it appears to add some blur to the picture. It's subtle, and not on the fast side.





Maybe this is a better example image so you can see what it does. 
http://thesis.mprazak.info/bilateral.jpg

As you can see, the original photo shows the girl with a lot of freckels and other skin details.
The processed photo has much of that removed, but the edges are still crisp. That's the 'edge preserving' part of it.