What makes for a good commentary? Some Q & A with Bible scholar D. A. Carson, Good thoughts and tips here, as commentaries can be poorly chosen, abused by relying on them too much, or neglected altogether.
How to Preach a Stale Sermon – sadly, it may be easier than you think.
HCSB Study Bible – one of the better comprehensive study Bibles available (along with MacArthur and the ESV Study Bible). On sale for $2.99 for Kindle. The iOS version is $9.99 and allows you to replace the HCSB translation with a different one (such as KJV, ESV) in case you’d like the benefit of the notes with one of the other translations they have available for the app.