Ok, so my game-money is pretty limited right now, the worst time that could happen!
I've got to choose between:

• God of War 3
• Just Cause 2
• Yakuza 3
• FFXIII

I think you're good leaning toward the first two, the others are a bit iffy, granted I've never played any of them, but from what I gather FFXIII has not been amazing, while I think Yakuza could be in a very select taste range. Personally I've already ordered Just Cause 2, and it's on its way, but I guess if you liked the first two GoWs, then the third is the way to go.

FFXIII is rather boring, not the freedom you had in previous entries of the series. Just cause 2 is PURE FUN, I havent had that much fun in a long time. I would go for Just Cause 2 to be honest :) God Of War 3 can wait, JUST CAUSE 2 CANT! :D

There are going to be so many FFXIII and GOW III on shelves in 6 months, so you could buy it used then for less.  I'd go with Yakuza 3 since it probably had a shorter print-run than Just Cause, but JC2 looks more actiony so if that is your current interest....

Just Cause 2.  You'll not regret it.  It has incredible replay value because it's a huge and hugely variant map with a ton of unlockable vehicles and weapons.

Final Fantasy XIII or Yakuza 3.

 Just Cause 2

Out of those I'm going with....FFXIII, that and GOW3 are the ones I've played out of those if I'm gonna be honest

Well you said you're leaning towards the first 2, so disregard Yakuza and FF for the moment. You can get those later. 
 
The choice is now between GOW and Just Cause. I'm not sure about your personal gaming preferences, but I can tell you that GOW has received slightly higher review scores. And I did notice you put this in the GOW forum, so to me that kind of seems like you've already answered your own question. Go with God of War 3.