First, let me just clue you to a rich resource for lectures, talks, and sermons online: Monergism.com. Most of the material here is free for download, and there are some great treasures made available.
After owning a burner for years, I finally decided to take the plunge and learn to use it last week. I was about to take a mini-retreat up in God's country (the Bishop-Mammoth Lakes area of California's Eastern Sierra Nevada), away from the other country (Sacramento). To make the drivetime most profitable, I decided to burn some sermons to listen to. So I was accompanied by the likes of Bruce Waltke, S. Lewis Johnson, Joni Eareckson Tada, John Piper, Sinclair Ferguson and others. What a rich blessing they proved to be.
Particularly let me single out to you the talks from John Piper's Desiring God Conference on Suffering and the Sovereignty of God. I listened to all except Piper's first sermon, and Carl Ellis' -- which is to say I heard John Piper, Steve Saint, Mark Talbot, David Powlison, and Joni Eareckson Tada. They were all helpful, all encouraging, all a blessing.
I have listened to Joni at least three times so far. Moving, encouraging, touching, chilling, humbling, heartening... I have often said that if I get to take out the garbage in Joni's neighborhood in Heaven, I'll consider myself well-off. What a remarkable woman. What a hard life; yet she bubbles with hope and encouragement and joy in Christ. I listen to her and think, "My brain is too small, my heart too hard and shallow" -- and I learn just a little more on each hearing. What's sticking now is her phrase, "The sheep-dog of suffering." Hear her, see what that means.
And Steve Saint -- it's an odd talk, not really very organized, just a little irritating here and there stylistically... and he pretty much had me sobbing. At one point I had to stop and say "No!" -- and deal with what he'd just talked about before going on. (It's true, I'm a softie. Tell no one.)
He's the son of Nate Saint who, with Jim Elliot and others, was slaughtered by the tribesmen to whom they were reaching out with Christ's love. Money-quote, from memory: "Why do we demand that every chapter be good, when God only promises that the last chapter will be good, and will make sense out of all the other chapters?"
I encourage you to hear them all. Thanks to Desiring God for being so generous with its rich resources, in a time when others are only making sermons available for money. It certainly was a blessing to this broken, struggling, redeemed sinner.
Other audio resources: