Hi ExJW,
There are several Commentaries that I've found helpful. One is the Ancient Christian Commentary on Scripture. This commentary has 29 volumes and covers both the Old and New Testaments, plus the Deutero-Canonical Books. Six of the volumes are on the Four Gospels. It's published by the InterVarsity Press, and is scholarly and conservative. An important feature of this Commentary is as the title says, it's commentary written by the ancient Christians.
The New Interpreter's Bible is a 12 Volume set with commentary on the Old and New Testaments and the Duetero-Canonical Books. This commentary uses both the New International Version and the New Revised Standard Version for the Bible texts. However, only two volumes are devoted to the Four Gospels. It's published by Abingdon Press and is scholarly and conservative.
You might also want to look at the Anchor Bible, now published by Yale University Press. The Anchor Bible is a new translation with commentary. The Anchor Bible has 8 Volumes on the Four Gospels. It's scholarly and liberal.