I stumbled across the Percolator app recently, and it's a lot of fun. It hasn't proved to be the most practical camera app I've ever used, but I find some of its interpretations of photos fairly stunning, and I think it could be brilliant in combination with other apps.
Percolator has three groups of settings: Grind, Brew, and Serve. Grind alters the relative texture size with four settings: Extra Fine, Fine, Medium, and Coarse. Brew defines the type of texture you want: Original Image, Circles, Overprint, Rings, Ishihara, and Full of Stars. Serve lets you pick from relative colour temperature and contrast options: Black, Light & Sweet, Soy, and Stirred.
Here's another example of Percolator's work:
taken with Camera and then run through PictureShow using the Mirror filter and an increased contrast level, and then run through Percolator using Extra Fine Grind, Original Image Brew, and Black Serve
I wouldn't use it for the average family vacation photo, but it's fun to create arty pieces, and who knows? Some of mine just might make it onto postcards or into some of my graphic design. I am looking forward to playing around with it in combination with other apps, because some of the work I'm seeing out there is fantastic.
If you want to check out what other people are doing with Percolator, they have a Flickr group you can join. There is some cool stuff going on over there that just goes to prove that an app in the right hands can be outstanding.