Message of Ecclesiastes (Bible Speaks Today) by Derek Kidner.
Ecclesiastes (Baker Commentary on the Old Testament Wisdom and Psalms) by Craig G. Bartholomew.
NOTE: I always benefit from Kidner's commentaries. This is a brief and accessible commentary that is useful for the general reader as well as for pastors and teachers.
NOTE: This commentary is scholarly, and extremely useful. Bartholomew's prose is crisp and clear. The nearly 100 page introduction is the best I've read, thus far. He surveys and critiques other commentators along the way without distracting the reader from the quest of seeking to understand the text.
Ecclesiastes (Tyndale Old Testament Commentaries) by Michael Eaton.
NOTE: This little volume is packed with content. Although it is very useful for teachers and preachers, it is a bit cumbersome for the general reader. I've been using this commentary along with others, but we recommended those in our Bible study group to use Kidner's book.
Time to Tear Down and a Time to Build Up: A Rereading of Ecclesiastes by Michael V. Fox.
NOTE: This commentary is also scholarly, and extremely useful. I'm using it alongside of Bartholomew, but feel that Bartholomew has extended the study in his commentary. I would recommend this as a supplement to Bartholomew's commentary.Ecclesiastes: Why Everything Matters (Preaching the Word) by Philip Graham Ryken.
NOTE: One of the other leaders in our group has been listening to some of Ryken's sermons on Ecclesiastes. This brand new titles is an edited print version of his expositional sermons. I do not yet own this commentary, but I received a notice from the Westminster Bookstore that it is now available and currently on sale. Ryken's comments have proven to be very helpful.Supplemental Studies:
The Wisdom of Proverbs, Job and Ecclesiastes: An Introduction to Wisdom Literature by Derek Kidner.
Five Festal Garments: Christian Reflections on the Song of Songs, Ruth, Lamentations (New Studies in Biblical Theology Vol 10) by Barry G. Webb.
A series of sermons we found most helpful are those preached by Rev. Ian Hamilton. These can be downloaded from the Cambridge Presbyterian Church website (here).