Washers and dyers are money makers. Even the oldest, ugliest working set will bring $150 minimum. I have always had good luck with them because people typically don't store large appliances unless they work. They typically sell within hours after posting them on craigslist. The other thing that sells fast is older used refrigerators. I think the reason cheap appliance sell so fast is that there is always someone out there who is just starting over. Also, there are plenty of people out there that live paycheck to paycheck and when their appliances go out, they need an immediate substitute.
This is a strange fact that I learned in the resale business: Cheap older appliances sell faster than modern used appliances. Especially in today's economy.
As far as mattresses are concerned, the law requires you to sterilize them. Some people do follow the law and others don't. Mattresses are great money makers, especially the name brands in good condition. I had no problem selling mattresses quickly. Obviously, if they're really sketchy, just get rid of them. But if they're in average condition, you will have no problem selling them from $40-$100. The nicer ones can bring even more.