FinFlow is an awesome program if you need to do any sort of cashflow or investment analysis. This includes mortages and other loans, as well as business or personal cash flows.
If you're a business/finances student or professional, you need this program. It makes variable cashflow calculations quick and easy. There is nothing else like it for the Mac or the PC.
Do read the manual though. Some of its functions are a little unintuitive at first. There's a method behind it, but there is a modest learning curve.