Some sites are legit, like intkeys.com. I used them to buy a copy of MW3 for Steam for only $21.50. They get ridiculously cheap prices by buying in bulk. I've never heard of keys4.me though, it may be legit too but I don't know.
Yeah, getting free games on steam from a Russian website is legit.
It's not free.
That. It's not free, you still pay.
IMO, if its legit, it's good. You'll have to jump through some hoops to get it activated though sometimes but they are pretty low hoops.