"Poison (Atheist Hip Hop)" by Tombstone Da Deadman (a.k.a. Rational Warrior) was used as the opening song of The Atheist Experience #699. The song starts with an sample of a previous show, in which Matt Dillahunty talked with Mark of the Austin Stone Community Church.
You can watch the original music video here:
(You can also download an MP3 of this song there.)