Answer: All of it.
Does that help?
Matt Perman writes at DesiringGod.org with a challenge to ministries to put all the sermons and articles and content they have on their website, make it easy to get to and give it away.
Make it Free: Improving Online Effectiveness by Removing All Barriers to Accessing and Sharing Content.
If you are a Christian media ministry, I commend the following vision for maximizing your effectiveness online: Post all of your content online, for free, without requiring registration, in a maximally usable interface.
This basis for doing this follows from the purpose of ministry and the purpose of a ministry website. The purpose of any ministry is, at root, to spread the message of the good news of God's grace. And the purpose of a ministry website is thus to serve as an avenue for spreading that message.
I suggest you go read the whole thing now as you consider what you should be making available on your ministry website.