A sermon prep aid that I have found incredibly helpful over the past couple of years has been the “Read the Greek New Testament” site by Peter Misselbrook. (http://www.misselbrook.org.uk/GNT/index.htm) The notes were first created when he taught students NT Greek. You need to have at least an elementary knowledge of biblical Greek, but for me at least it provides just the right amount of help. The Greek text is laid out verse by verse, vocabulary beyond the very basics are identified (including verb declensions) and some commentary notes if they relate to the text are laid out. He gives bibliographic information about the commentaries at the end of the introduction to the book at the beginning of each NT book.
I have Libronix and LOVE it, but I want to improve in my Greek as I prepare sermons and this allows me to do my own translation, allthewhile checking with some standard commentaries. (I am presently preaching through I Corinthians and the works he cites are commentaries by Leon Morris, John Drane & Anthony C. Thistleton.) While it is not designed specifically for sermon preparation (it is designed, as the title suggests to “Read the Greek New Testament”–the text is broken up into daily manageable chunks), I find it useful that way.