As someone who doesn't like to travel with more than just a computer bag, it's a sad situation to completely ruin a favorite pair of black pants that didn't wrinkle and fit better than any others.
Real Simple magazine (Nov. '09) has these tips for black pants: (for those who don't want the time and cost of eternally dry cleaning)
1. Don't wash them as much. Wear 4-5 times between washings.
2. Turn pants inside out to minimize color loss.
3. Choose a short, delicate cycle.
4. Use specialized detergent for cold water loads, such as Tide Coldwater. Chlorine in tap water is apparently "color-sucking."
5. Hang or lay the pants flat to dry. Don't throw them in the dryer.
6. Buy pants with fabrics that hold dark dyes well - washable wool blend or nylon.
RIP, favorite black pants.