I'm by no means an expert on Crossed Out, but I can relay what I know. They existed from 1990-1993, and are credited by many as starting the whole power violence thing. Many bootlegs abound, and original pressings of their records are sold for silly amounts of money. The release of this CD/LP might save you some cash, as it's a more than complete discography, including demo tracks, live stuff, and practice recordings. Forty-seven songs in forty-five minutes.
It's easy to hear the influence they've had on a multitude of speedy hardcore bands nowadays and why. Extremely fast straightforward hardcore with all the right breaks and blastings and biting, no-nonsense lyrics. Seven years gone and still fucking right-on.