Craig Keener's "Acts An Exegetical Commentary" is a must-have for all those doing research into Acts. It has a particular emphasis on background material and, with four volumes, it is able to go into much greater depth than other commentaries. While I will go to other commentaries for quick reference and for text critical questions, Keener's volumes will be my most valued resource on Acts. He writes clearly and considers many sides to every question, and is generally cautious in his conclusions.
Particularly important is Vol 3 p2350-74, where Keener discusses the use of the the first person plural in Acts. He surveys styles of self-reference in ancient writings and concludes that when ancient historians used first person narrative ("I" or "we"), they did so to show that they were present at the events. The style of self-reference in Acts, Keener shows, is no different, except that Luke's Judeo-Christian humility prevents him from naming himself or using first person singular as much as other writers. Luke was a participant in the events where he uses "we", and he was probably also present for other events that he narrates (Keener thinks it likely that Luke was in Judea during the time of Paul's imprisonment there (Acts 21-26)). Keener's conclusions are almost identical to mine (see here), and he has the same concerns as I do about William Campbell's inferences.
I intend to interact with Keener on other issues in my next blog posts.