Pennsilfaanisch, or Pennsylvania German, is a dialect of High German native to the American state of Pennsylvania. The language was widely used in southeastern Pennsylvania, especially in rural areas, up to the 1950s, but has since then been in decline. Nowadays, the majority of speakers are actually Amish or Mennonite, and the language is seen as particular to these groups, even though historically they only comprised a minority of its speakers.
I personally do not know the language (and I'm not of German descent either), but I grew up in a region where it is spoken and have had some contact with it, primarily through weekly farmers markets. I'll be moving back to the region in January for university, and some places in the region have classes for the language, so I might take one.
Here are some resources I have found online for the language:
http://archive.org/stream/cu31924027513 ... 5/mode/2up
http://home.ptd.net/~tconrad1/dutch_main.html
http://faculty.kutztown.edu/equinter/
http://archive.org/stream/commonsensepe ... 7/mode/2up
http://hiwwewiedriwwe.wordpress.com/