Christian audio is making a collection of 27 tracts from Crossway Good News Tracts available for free. These tracts come as both audio files (about 5 minutes each) and PDF files.
I have not read them, but a glance through the titles and authors (and the publisher) makes me think these will largely be trustworthy tracts.
This looks like a good deal (but only if we use them with non-believers!).