Jesus Christ returns on May 21, 2011. You'll definately want to mark this date on your calendar because, you know, if you're raptured, you don't want to leave a kettle on the boil or the bathtub water running. It might cause problems for those who are Left Behind.
Anyway, the folks who are blowing the trumpet and warning the people (Ezekiel 33:3) of the impending Day of Judgement are the owners of Family Radio, Inc, a Christian radio network with a nationwide audience. It's founder, Harold Camping, has precisely calculated the date of the Rapture using clues in the Bible.
One of 40 billboards in 8 states warning of the impending Day of Judgement.