This person has put together an excellent list of high quality articles regarding the Penguin update with a brief key point from each article:

9 Resources for Learning About The Google Penguin Update - Sparkplug Digital


Two of the best articles I have read about this Algo change that are included in the list are:

What to Do if Your Search Rankings Were Hurt by Google's Penguin Update

Penguin Analysis: SEO Isn't Dead, But You Need to Act Smarter | Microsite Masters

Here is Another Excellent resource:
Google Penguin Update - History, Diagnosis and Recovery