Asteroid 1950 DA was discovered in 1950. It was rediscovered in 2000. It visits the Earth about every fifty years, and after fourteen more of these passes by, on March 16, 2880, it will be making a really close one.
How close? Closer than the moon. The current estimate is that there is a one in three hundred chance of an impact with the earth. Not much of a chance, but a lot more than the chance of me winning the Big Game lottery this weekend ...
Here's a Wired News article on the matter.