Prints leaning to side

Well... I'm still calibrating my new MendelMax and aside from other minor problems, I have this leaning problem.
All of my prints are leaning to one side.
My setup:
Arduino Mega 2560 with RAMPS1.3
Sprinter
Skeinforge
Repetier-Host
all driving a MendelMax

I have tried trimming the potentiometer on the Pololu drivers, following some tutorials (I tried this like thoudand times...), tightening all belts and screws (nothing wobbles even a little), moving the PC closer (I had quite a long cable leading to the Arduino from my PC), using another PC and I have even checked, that the motor doesn't have trouble pulling the fillament when moving from side to side.
Now I'm completely lost and all my prints are completely useless as I want to use them mainly for construction, so I require at least some precision.
Please help!
I do also have trouble with oozing and stringing and the start of a thread getting not enough fillament, but that is only minor as I now focus on fixing this.

Photo attached (hope you can see the problem there).

Can you print something tall and thin, and take a picture of that from the side, it's not easy to tell what's going on in your pics!

I am sorry, I have probably not expressed myself properly. The prints are not leaning from the vertical, but from the horizontal Y axis. The right angles of the cubes are not right. But I hope I have solved this problem already as I realized that I forgot to put the X axis precisely in the middle of my Max, so the angle included by the Y and X axes is not right, therefore the prints are not right-angled as well. So to anyone having the same problem: Check that your axes include a right angle!
Thanks for the reply, anyway.