It seems that the past couple seasons of The Simpsons have really done a lot with their couch gag during the opening sequence. They have also been adding a new gag somewhere in the opening sequence with every episode. It is no longer just Bart's writings on the chalk board that changes.. Most notably in recent time they have had opening sequences "directed" by graffiti artist Banksy and animation director John K. (videos posted below)
The latest opening sequence was animated by one of my favorite animators and director Bill Plympton. It has his signature style and look. Nothing short of spectacular. Bill Plympton will also be featured in an upcoming Cartoon Round-up post.
Here is the opening sequence animated by John K. and a great article here about the whole thing by Amid Amidi on Cartoon Brew.
The Banksy sequence ruffled a few feathers. Here is an article about this sequence from Amid Amidi that he posted on Cartoon Brew.