I get a lot of questions about podcasts. There are so many on iTunes now that many have a hard time finding those worth listening to, so, in my opinion, here are a few that are well worth your time:
1) Andy Stanley at North Point. I don't always agree with him and prefer expository preaching but generally he is very good at taking fairly difficult concepts and converting them into sermons that nearly anyone can understand. Few dislike him and seminary nerds like me can learn from his approach and style.
2) Mark Driscoll at Mars Hill. Driscoll is Reformed, Evangelical and direct. He preaches through books of the Bible and his sermons last for an hour or more but its great stuff.
3) John Piper at Desiring God. Piper is the man. Passionate and intelligent. A true pastor/scholar (he has a Ph.D. in New Testament from a respected German University and taught Biblical theology at Bethel Seminary for more than 5 years). Check it out. He yells almost as much as I do!
4) Ravi Zacharias at Let My People Think. A half-hour weekly podcast normally part of a lecture series from the master Christian apologist. I love it.
5) Allister Begg at Truth for Life. Great Scottish preacher. Half-hour podcasts posted daily. Check it out.
There are many others worth perusing like Francis Chan at Cornerstone, Erwin McManus at Mosaic, Matt Chandler at the Village, Joshua Harris at Covenant, etc. But the first five are good places to start. Enjoy and may God bless,