While some manufacturers say it's OK to put your frying pan in the dishwasher, many recommend against it for several reasons. Contrary to what you might think, it's actually better for your pans to stay a little oily, as it helps prevent food sticking. This is why gentle handwashing is ideal for most pans. Handles can also be knocked about in the dishwasher, and the chemicals used aren't always a frying pan's best friend.
Cast iron should never go in the dishwasher, as you'll strip away the 'patina' of oil, and will need to re-season your pan. Non-stick should only ever go on the top shelf of the dishwasher, further away from the heating element at the bottom of your machine. Stainless steel is more durable, and will usually be OK in the dishwasher, but again, it may shorten the pan's lifespan.