A lot of good sermon material is freely available on the internet. John Piper's sermons are available in text, audio and the later ones in video format.
Other speakers choose to sell their talks, but may give some away.
Tim Keller, of Redeemer Presbyterian Church, New York has a few that are provided freely, and the link points you to a collection of 150. The titles are intriguing. If the talks are as as good as the titles, they should be terrific.
I have usually found his messages to be easy to listen to and faithful to the Bible's message. I am expecting this is the case with this collection.