Many people have found that commuting by bike has caused them to show up to work with grease stains on the inside cuff of their right leg. This is from the cuff hitting the chain with each puch of the pedals. Fortunately, this can be prevented.
One of the easiest ways of preventing the pants from hitting the chain is by securing them to the rider's leg. Many people have used a simple tie over the years. In recent years, with the advances in popularity of commuting by bike, a number of companies have come out with pant protectors.
These accomplish the same thing as a tie but are specifically designed to stop the chain from hitting the pant leg. A simple cuff works well enough and is very popular. There are other items, however, the protect the majority of the inside of a person's leg from the grease. This option protects more of the pant from the chain.
Overall, pant protectors will save any commuter money (less dry cleaning bills) and time and not force them to look ridiculous when they get to work.