Wonga makes it simple.
Sometimes you come across something that just feels right. Wonga (www.wonga.com) is one such something for me. I don't mean the business model of lending people small amounts of money at relatively high interest rates over short periods. There are arguments both ways on that one, and I'm not going to express a view one way or the other on the merits of such "pay-day loans". What I mean is the way the Wonga website presents that idea and lets you immediately interact with it.
You can try it for yourself. Two sliders let you change "how much cash you want" and "how long you want it for", and you immediately see the resulting interest, fees and total repayment change before your eyes. There's no form to fill in. Not even a "recalculate" button. It works in real-time as you slide the sliders back and forth. The result is a three-fold benefit.
Mental model: If you borrow more, or borrow over a longer period, you'll pay more. That's obvious to some people, but this interaction makes it viscerally clear to everyone.
Aesthetics: The simplicity and clarity of the design rubs off on the provider. The interaction is transparent and honest, so the lender must be too, right?
Simplicity: Wonga doesn't offer anything else. There's no attempt to sell payment protection insurance, longer-term loans, or anything else at all. Just the one clear proposition. Product editing at its finest.
Once again, I'm not here to endorse (or oppose) the product. Wonga apparently has some very sophisticated algorithms and heuristics under the covers to decide who they'll advance money too. But the design of this interaction hides all that, and puts the proposition into the very best light. That's what I like.
Of course, I did read that their algorithm is so sophisticated that it actually pays attention to the way you play with the sliders before you apply for a loan, particularly if you immediately whack them both up to the max. Oh dear. Bang goes my credit rating. And yours too now I expect.