This is probably old news to you, but it's new news to me and my ancient Egyptian ancestors told me during my hypnotherapy that the entire universe is just a figment of my imagination, therefore I can post it if I please and if you moan it's only because I'm imagining someone moaning. Cloud gaming tech Gaikai has been offering streaming demos of various games - most notably Dead Space 2 and Mass Effect 2 - here and there for a while now, but I've just discovered that, over on Eurogamer, you can jump into browser-based slices of Crysis 2, Magicka, FIFA 12 and the Witcher 2.
Update: omigodomigodomigod. There are more demos on the Gaikai site. Including FARMING SIMULATOR. Yes! Also, try this link if you're being region-blocked on the other. It might work: hard to say without catching a few jetplanes to the other side of the world.
Gaikai different to OnLive in that this is just to promote the full, traditional version of the game rather than be main event in itself, and it's pretty good way of achieving that even if there is an inevitable hit to visual quality and control smoothness. Clever stuff, but looks much nicer in a window than fullscreen.
Oh, and Crysis 2 seems slightly laggy even when running on a massive PC elsewhere, bless it.