John MacArthur - When the good folks at Grace to You made every MacArthur sermon downloadable for free, we all in one voice praised the Lord who answers prayer. If you are preaching from the New Testament, MacArthur has preached from it himself. For me, this is where every preacher should begin.
The Gospel Coalition - Although TGC has removed a large number of their sermon archive, this still remains an invaluable tool. Some of the pastors featured here include DA Carson, Tim Keller, Kevin DeYoung, Thabiti Anyabwile, Ligon Duncan, Russell Moore, and others.
Kevin DeYoung - DeYoung is one of the brightest young evangelicals today. His sermons are always insightful.
Monergism - Like TGC, this is a great resource to discover a host of great sermons and preachers. As the name suggests, all speakers and articles are exclusively from a hard Reformed position. One advantage, however, of this resource is that it includes classic sermons from the likes of Martin Luther, Charles Spurgeon, and others.
Russell Moore - Dr. Moore is one of my favorite preachers today.
Albert Mohler -Mohler is one of the best thinkers of our time. Though he does not preach weekly, he preaches regularly in a variety of pulpits. In addition, he teaches a weekly Sunday School class that is recorded.
Alister Begg - Begg is a preacher and not just because he has a Scottish accent.
Ligonier - Though this is primarily the home of all things RC Sproul, it isn't just that. Here you'll find great resources from others like Steve Lawson and Sinclair Ferguson.
Martyn Lloyd-Jones - Although I don't listen to MLJ much, he certainly remains a very influential voice.
Mark Dever - Great exposition. Dever exposits both individual passages and even entire books.
Hershael York - The head preaching professor at the Southern Baptist Theological Seminary.
Matt Chandler - a popular pastor in Texas that I frequent.
JD Greear - Like Matt Chandler, JD Greear is a popular pastor who is gaining in popularity. He is more than likely the next president of the Southern Baptist Convention.
No doubt more could be added and I will likely add to this list in the future. But certainly this is more than enough. Use these sermons and resources as a means of improving your exegesis. God has blessed us with this great tool, let us utilize it (without plagiarizing of course) in order to serve his people.