What Games That Works On Steam And Origin With the Same Key?

Probably not. Origin is EA's way of saying they want to be rid of steam.

my dead space 2 bought on steam magically appeared on origin without me doing anything...

My mass effect 2 activated on orgin

Shame it doesn't work the other way around though. :-\
Alice: Madness Returns would be another one.
And +1 to it working with Mass Effect 2 as well.

Battlefield Bad Company 2 bought on Steam also gets you Limited Edition version of BFBC2 on Origin.

Most EA games purchased on Steam also activate on Origin.

I got Shank, Dead Space 2 / Medal of Honor as the same key

but where do you get the keys for these games? Some of them have it on the cd-key section but others do not?

If you buy any EA game on STEAM, you can use it on Origin.
But you can't use Origin keys on STEAM.
If you have old EA games on STEAM(like Mirror's Edge or Dead Space) you must look for keys in data files.

My shank from hib 4 and spore are redeemable on origin too

If you use the same EA account for Origin and EA games, games will be sync in your origin (at least for me, after installing MoH and BC2 on steam they came out on Origin too, without doing anything)

its the same shit with gfwl, you can activate 30 games with 1 key luls

• Battlefield Bad Company 2
• Burnout Paradise: The Ultimate Box
• Crysis Warhead (but no Crysis)
• Crysis 2
• Mass Effect 2

Origin Code Redemption FAQ