Over the years, many films have featured really great opening cards. I can think of two right off the bat.
The Texas Chain Saw Massacre begins with this legend (both lettered on-screen and read by John Larroquette):
"The film which you are about to see is an account of a tragedy which befell a group of five youths, in particular Sally Hardesty and her invalid brother, Franklin. It's all the more tragic in that they were young. But had they lived very, very long lives, they could not have expected nor would they have wished to see as much of the mad and macabre as they were to see that day. For them, an idyllic summer afternoon became a nightmare. The events of that day were to lead to the discovery of one of the most bizarre crimes in the annals of American history, The Texas Chain Saw Massacre."
Another truly great (and elegantly terse...) opening card came from The Blair Witch Project in 1999:
"In October 1994, three student filmmakers disappeared in the woods near Burkittsville, Maryland while shooting a documentary. A year later their footage was found."
Of course, in cinema history, everything (even title cards) boasts a precedent or antecedent. Compare that Blair Witch opening card with this one, from Peter Weir's 1975 masterpiece, Picnic at Hanging Rock:
"On Saturday the 14th of February 1900, a party of school girls from Appleyard College picknicked at Hanging Rock near Mt. Macedon in the state of Victoria. During the afternoon several members of the party disappeared without a trace..."
Of course, not all title cards are created equal. Here's one from the canon of one of my personal B-Grade heroes, the late, great William Girdler. In particular, it comes from Day of the Animals (1977):
"In June 1974, Drs. F. Sherwood Rowland and Mario Molina of the University of California startled the scientific world with their finding that fluorocarbon gases used in aerosol spray cans are seriously damaging the Earth's protective ozone layer. Thus potentially dangerous amounts of ultra-violet rays are reaching the surface of our planet, adversely affecting all living things. This motion picture dramatizes what COULD happen in the near future if we continue to do nothing to stop the damage to nature's protective shield for life on this planet."
And below is the opening card from Embryo (1976):
"The film you are about to see is not all science fiction. It is based upon a medical technology which currently exists for fetal growth outside the womb. It could be a possibility tomorrow...or today."
And lastly for today, here's one from Sssssss (1973) [don't say it; hiss it...]. This one practically shrieks "lawsuit" and "litigation":
"All the reptiles shown in this film are real. The King Cobras were imported from Bangkok, the Python from Singapore. We wish to thank the cast and crew for their courageous efforts while being exposed to extremely hazardous conditions."
So, read any good (or bad...) opening cards lately?