How Will We Be Judged?

Will God judge us based on our intentions or on our beliefs and actions? In other words, does there exist an absolute standard by which He will judge us?

If it is absolute, He can not arbitrarily evaluate one person on his intentions and another on his actions. If this is the case, it is problematic when carried out to its logical ramifications. If God judges everybody based on individual intentions, I don't see how He could condemn an Islamic terrorist hell-bent on killing innocent people if this person genuinely believes he is doing so for God's glory.

On the other hand, if God judges us based purely on our beliefs and actions, He would out of necessity have to condemn a retarded cripple only because his misfortune, through no fault of his own, precludes him from harboring a cogent belief of any sort and from doing anything worthwhile for God's sake.

Now obviously many will arbitrarily claim He will judge some based on intentions and others based on actions and still others based on a combination of both. But how would anybody know by which standard he himself will be judged?