I think these things have already been said in this topic, but this is my opinion:
I think that people shouldn't play god (I don't believe in god and you know that.. so I'm not saying that god would be angry at us coz we're playing god or anythins.. What I'm saying is that we have no right to decide who lives and who dies.)
I think it's wrong to kill a person despite of the fact that he or she is a murderer or other dangerous criminal. Killing the criminals surely ensures that they will never commit any crimes again and that's a good thing, but killing a man surely isn't.
What comes to the "an eye for an eye"-opinion.. If someone kills and we decide to kill him we aren't any better persons than the killer. I also think that the criminals get off too easy if they are executed. They should be held in prison for the rest of their lives and suffer for the crimes that they committed.
Though life in prison doesn't really mean a life in prison..

If someone commits a terrible crime and he's convicted for life he can walk free after 14 years if he's been nice and stuff. Or if the president lets him go. That just sucks!
And Dan.. Here in Finland I would say that the prisons are luxurious. You have your own room and loads of furniture there and you've got tv and books and stuffs and you can study in there.. But you don't have your freedom. But to some people it doesn't really matter..
Oh yeah.. and now.. we've got these "prison" villages where the criminal mother or father can get a detached house where he or she can live with his/her children.. And they call that a prison..? zees..