The most simple business to start is one that you already know how to do. People don't buy what's essential, they buy what they want to buy. One person may consider a 64" flat panel monitor is essential, whereas someone else may think a 20" is essential. It's all relative.
And "lots of customers" isn't specific, which you need to be when considering a business. A small airline may consider 50 customers a year "lots of customers" if they are selling private memberships at $300,000 a pop. Another company may need 300,000 customers which is "lots" to them.
Until you consider what you have to offer in the marketplace, we're at a loss how to help you.