OFM responds to a query about reference works:

   [Aside from a commentary, you might also want to consider an
   introduction.  These are books intended for use in undergraduate Bible
   courses.  They give historical background, discussion of literary
   styles, etc.  And generally they have good bibligraphies for further
   reading.  I typically recommend Kee, Froehlich and Young's NT
   introduction...

Two other Intros to consider:

The "Introduction" by Ku:mmel is a translation of a strandard NT text.
The references are slightly dated and the style is somewhat dense, but
the book contains a wealth of information.

Perrin and Duling's Intro is also very good.  It's somewhat more
modern than Ku:mmel's but not quite so densely packed.  Also the
authors tend to go through the books of the NT in the historical order
of composition; this gives a very useful perspective on the
development of the NT.

   ... There are also some good one-volume commentaries.  ... Probably the
   best recommendation these days would be Harper's Bible Commentary.

A slight dissent: I think the Harper's is "OK" but not great.  One
particular problem I have is that it tends to be pretty skimpy on
bibliographic material.  My feeling is that it is OK for quick
look-ups, but not real useful for study in depth (e.g. I keep a copy
in my office at work).

   ... (I think there may be a couple of books with this title...

So far as I know there is the only one book with this exact title
(James L Mays, general editor, Harper and ROw, 1988) although I think
I recall a (older) series under the name "Harper Commentaries".  Also
there's a separate Harper's Bible Dictionary (most of my comments on
the HC also apply to the HBD.)

My favorite one-volume commentary is the "New Jerome Biblical
Commentary".  The NJBC is rather Catholic in focus and somewhat biased
towards the NT.  (The reader can decide for her- or himself whether
these are pluses or minuses.)  In any case the scholarship is by and
large excellent.

NOTE: The NJBC is a completely reworked, updated version of the
"Jerome Biblical Commentary", copies of which can still be found on
sale.