I think that in order to analyze this to the fullest, I want to separate a few things that I consider to be different yet connected (maybe confusing now, but hopefully by the end it won't). All of them are different interpretations of free will (or lack thereof) that I can think of.
Determined Destiny: This is when, no matter what happens, something will always have the same end result: ex. 1+3=4 2+2=4. Although I use different numbers in either equation, you still get 4 in the end. I think that this is the kind of thing where, you are told that you are going to die, so you become more aware than you would have if you weren't told that you were going to die. Because of that, you notice the hole in the ground, but then as soon as you step around it you get struck by lightning and die. Whether or not you see the hole, you're going to die anyway.
Only One Real Path: This is pretty much the ultimate of non-free will. There is only one way that anything can ever be done and nothing can ever be changed. You are asked a question a million times and you always answer 'no'. This is because something has a plan for you and you always will do the same thing, no matter how many times you can re-do it.
Only One Path, But You Are Paving It: Everything can ultimately be boiled down to a 'yes' or 'no' answer, 1 or 0, black or white. Either the path goes left or right, regardless, it is up to you in a 'spur of the moment' decision on which direction you will go, which will, ultimately, lead you to wherever you will end up in the end. I suppose this is the option that people who believe in free will will choose.
Ultimately, however, none of this philosophical discussion will ever matter, because theres no way that you can ever prove or disprove either of the assertions because there is only one way that reality goes in, whichever one it is, which is the only thing consistent with both arguments. But then, essentially, both the arguments are the same because that is the substance behind either one; that time only goes in one direction, no matter which direction it is.
Because of that, the decision is essentially up to whoever you're talking to and what is more comfortable to them. I, personally, choose to believe that I have a choice in what happens in my life, you know, life is whatever you make of it, so make sure you make it good. I think that most of the theists here believe that there is no free will because they want to believe that there is an absolute meaning for your life, no matter what happens in it; God made your life the way it is because he thought that it was best. This is another example of one of religions few benefits; that people can feel good about themselves because they know that there is meaning in what they do.
Well, anyway, I think I'm done for now. Sorry for the uninterpretable gibberish that may have resulted from my ramblings... Anyway, I hope that this will help with the discussion in some way...
EDIT: After thinking about it, I don't think that I really provided an actual explanation of why you can never prove nor disprove free will. The reason is because, regardless of which option is chosen, that option and only that option is chosen. Since the choice happened in the past compared to when people actually analyze it, that option is the only option that could ever have been chosen, because then it would alter the future that the observers are now in, which isn't possible. Either side could play it off as either free-will or destiny, because they can't go back and re-do it to prove otherwise. Oh boy...I dunno why, but I feel like I just opened up a can of worms... Oh well, I'll leave it to you guys to interpret it however you will.
used so that a criminal identified as sane can be tried as a premeditative felon.