When I first started out preaching and teaching Isaiah, there were very few good commentaries on Isaiah. In the last fifteen years or so there have been some excellent new additions:

• Alec Motyer's long commentary is very detailed and requires hard work but is thorough and rewarding. 
• Alec's shorter Tyndale commentary is much more accessible and also very helpful.
• Since I started work on Isaiah, I have come across John Oswalt's two volume commentary on Isaiah (NICOT). It's good and accessible given its depth.
• Not surprisingly, he has also produced a more condensed version in the NIV Application Commentary series. His volume is an excellent contribution to this series.
• For groups and study guide Barry Webb's BST commentary is also very worthwhile.

[Editor's note – we would also include, of course, David's new volume Teaching Isaiah.]