The Gospel Coalition website is proving to be a great resource for Gospel centered text, audio, and video resources. You can browse resources by the name of the author/speaker, topic, or Scripture reference. In addition, you can browse for specific types of resources such as sermons, articles, interviews, etc.
If you're looking for a place to start I suggest you listen to or watch D.A. Carson's lecture entitled "What is the Gospel?". You can find the audio and video here or in iTunes.
Ryan Wentzel