Walk down the street. Every business you see that isn't closing down is doing things people want.
Go online. Find out what people are searching for. Look at the vendors who provide those products/services. Figure out how to do it better/differently/more efficiently than them.
Make up random word combinations that seem likely and google them. What businesses are built around those concepts? Are there forums where users congregate online. I remember in one of Spolsky's podcasts he made up "software for the rubber industry, or something." I used to drive by Rubber Industries Inc. every morning and chuckle to myself. There is no concept so strange that someone hasn't made a business of it yet.
Coming up with business ideas should be nothing short of trivial. The hard part is finding something that matches your skillset and interests and that is used by a customer base you can reach cheaply enough. It doesn't have to be world changing or incredibly technical: people make millions of dollars washing cars for pete's sake! I'm sure the car washing business needs software!