The latest list of "The 100 Best Companies to Work For in America" is available now at Fortune's website (subscription required). For more information on this list, see the Great Place to Work Insititute's website - they do the underlying research.
There are many lists of great companies, but this is one of my favorites. It is one of the longest-lived (the first book came out in 1987) and is based on thoughtful and original research, not impressionistic analysis or press clippings. And it feels intuitively right to me - I have visited many of these companies, and they really do seem to be superior workplaces, and, often, superior business franchises.
In 2002 Chris Luck and I did a study and found an equal-weighted portfolio of the publicly-traded companies on the list would have had returns a little better than those of the S&P 500, even after accounting for valuation disparities, industry exposures, and other risk factors.