Andy Beal writes that Microsoft Acquires Jellyfish – Apparently Shuns Peanutbutterfish and one thing about Jellyfish that's different is they pay you to shop.  According to Beal:

"…You mean, I get paid to shop? Where’s my wallet?

Here’s an example search result, complete with details of how much you’ll get back in cash…

The great thing is, this is not just some gimmick for Jellyfish, they’ve actually given a lot of thought to their business model.

At Jellyfish, we want to pioneer a new form of search advertising we call Value Per Action. Instead of charging fees when you click, we charge our advertisers only when you actually buy, and we share at least half of this fee back to you as cash back. In other words, we connect you directly to the value of the advertising. Instead of measuring how much money WE make when you click, we measure how much value the advertiser is willing to pay YOU for your sale. With VPA, the advertising value of your attention becomes transparent (you can see it in the form of cash back) and changes from annoying advertising into something that actually lowers your end price."

I guess this works if you shop a lot online (and have the money to spend); I would not bother with it otherwise, but that's just me.