Gaikai that's looking to partner with online retailers, Walmart.com seems like a pretty good option. (In case you're reading this on a mobile platform that can't see italics, we put them on those last three words to emphasize that were were understating the point. Classic Joystiq!)
The retailer has, according to VentureBeat, added Gaikai in-browser game streaming to its GameCenter page for Dead Space 2 and possibly other titles. At the moment, none of us on staff can see the option to stream the game, but we know it's automatically disabled if you don't have the requisite bandwidth. Maybe we all just need to get fatter pipes?
Assuming it'll all work as designed sooner or later, this could set a pretty important preceden for online game shopping. We just selfishly hope you'll still read our reviews when Skynet lets you try everything before you buy it.