They're called PlaystationNetwork Cards. They are available in the USA and Japan but not in Europe so far :(
They don't give you points however. Think more on the lines of topping up your payg mobile phone or like a gift card you'd use for iTunes you buy a $20 card which will give you $20 to spend in the Playstation Store. There are rumours in place that these cards are on the way to Europe but don't expect them soon, or even next year.
there may be a way around this.
Make a new PSN account on your ps3, make it American, you'll have to fake the address and postcode, i used the Beverly Hills 90210 zip code (it really exists) once you've made your American account, when you sign into the playstation store, it will be the american store which has different content on it that works on a euro ps3, they've got rag-doll kung-fu fists of plastic for free just now :)
Then, all you have to do is find somewhere online that you can buy a psn card from, amazon etc etc, buy your card, input the code and you're ready to shop on the psn.
I have an American account set-up but I've never bought anything from the store this way but there's no reason why it shouldn't work.