Define three categories of business entities that would have a use for a SaaS offering. For example (and you can't steal mine): a local dentist office, a legal firm, and a tax office. Determine what regulations could exist, be it government, industry, or otherwise, regarding the control of data.
Once you've determined your three categories, find three unique SaaS offerings for each business. For example, my tax office could use: QuickBooks online, Constant Contact, and Google Apps. Justify or define what each app is, what purpose it serves, and why it is a value added for the business. What cost benefits and disadvantages are presented by using a SaaS offering as opposed to an in-house system?
Once you have found your 9 SaaS offerings, compare and contrast where they could be used. For example, for regulatory reasons, a legal firm probably wouldn't use Google Apps.