Noise from crankshaft spindle and then the pedal falls off In the last 6 months I have been getting really bad noises, creaks, clunks, etc coming from somewhere around the spindle connecting to the crankshaft. Every time I put pressure down on the left hand pedal, either it or the spindle attaching to the pedal creaks, clunks real loud and then the pedal works itself loose. I have tightened it up every time and after a couple of days it becomes loose and almost falls off again. Can anyone help explain why and how I may fix it myself?

Sorry actually being a bit clearer it is the square taper crank arm that comes away from the spindle. The pedal actually is fine. The bike is an Dawes XC 2.2 and the crank arm has "Truvativ" Powered by SRAM on it.
Like I said, by now the crank arm is toast.  Originally the problem was just that the crank bolt was loose (they need to be REALLY tight -- ideally set with a torque wrench). 

But running with a loose crank has deformed the socket on the end of the crank to where it no longer fits, and it rocks and works the bolt loose as you pedal.  And by now the crank shaft (which is steel vs the aluminum crank arm) may also be deformed.

There is a vague possibility that a clever person could make the existing crank arm work fairly well with a shim cut from a beer can, but it takes some mechanical aptitude.