Do you believe that some actions are unforgivable? If so what are they and why are they unforgivable?

Murder, because no one has the right to take another person life no matter what. We weren't put on this earth to kill each other.

Despite my past, I have to agree with Inu. Murder is about as bad as it can get. No matter what happens to you in life, at least you can recover from it, you can look on the bright side, you can rely on your friends to support you. When you're dead, you're dead. That's it.
We have very little control over these short bursts of experience, and noone has the right to end yours. It ends when it's supposed to end, not when some jerk wants revenge/money/whatever.

The only exception I see to this is euthenasia, which I only believe is okay if they have the capacity to give you permission. If I'm using the wrong word for assisted suicide, then yeah, that's what I mean.
Anyway, if you're going to die shortly anyway and you'd rather end it than live in blinding, maddening pain, then I believe you have the right to ask someone to end it.

Euthanasia is not murder. Not all killing is murder.

I agree, but your point interested me anyway. What kind of killing do you consider murder? For example, is war organized murder? Or just organized killing?

And I'm not sure what I consider unforgivable. I don't know that I consider murder unforgivable, because everyone has their reasons, and some of them are damn good reasons, but usually when someone has such a reason it's not considered murder, so...it's kind of circular.

Killing combatants is not murder, but killing innocents is murder.

Murder is the unlawful killing of another, especially with premeditated malice.
(Dictionary.com)

War is not always murder. It's not black and white; there are gray areas.

If you use soldiers to slaughter innocent people, is murder.
Killing other combatants/soldiers is killing.

I don't think premeditated murder is a damn good reason.
You deliberately end someone's life.
Myke puts it (and I agree):

If you have a huge beef with someone, something you feel you can't get past, it is still not good enough to end another's life.

I also think that rape is unforgivable, because it can really screw up a womans life or a guys. Its something that can't ever really be forgotten. It messes a person up, no one should have to go through something like that.

Talking during the theatre. It is unforgivable.

Likewise, I do it all the time, so I really don't have much place to talk.

In truth, I define only two unforgivables:

Murder and rape.

Murder? Well, for obvious reasons. What is stolen can be returned. What is broken can be mended. What has been harmed can be healed. A life, once taken, can never be restored.

Rape? As emotional distress goes, rape is obviously a huge hit. It scars people for life, and it far more destructive than other "sins", as it were. Although the emotial pain caused can be eased, I don't think it ever goes away. That sort of pain always lingers, or at least I can assume. I've never had it happen to myself, and I never plan to, so I really can't say, but I can assume.

Ah, though it may be unpopular, I don't believe that there are unforgivable sins. Not to sound preachy, but in the Bible it says:

God is willing to forgive any sin, no matter the degree, if you will confess it to Him. That does not mean, however, that the sin will go unpunished. If you murder someone, you deserve to go to jail. If you rape someone, you deserve to go to jail longer (IMO). Different sins have different consequences, some that will affect you for the rest of your life.

I could go to the store and steal a pack of gum, and if I'm caught have to pay for it. God will forgive me of that sin if I ask Him. I could go get a gun and shoot and kill someone with it, and if I'm caught go to jail for it. God will forgive me of that sin if I ask Him.

Now, that does not suffice to say that I can "First John One-Nine it", and just sin and ask forgiveness later. Sin separates us from God, and everytime we sin it becomes harder and harder to come back to Him.