Where can I find the planned and flown paths for certain flight routes? Are there official definitions of air traffic corridor pathing? Specifically European &amp; Mediterranean routes. 

I'm working on an application that needs this input data to perform an analysis. I and others in my company have been unable to find anything, and I really don't want to have to derive something approximating it myself if I don't have to.

Edit: Since what I'm asking for doesn't seem to be very clear I'll try a different way.

When an commercial jet starts a flight from one airport to another. I assume it had a generally predetermined path (or options of paths). These are not straight shortest path between two points on an ellipsoid so the data at OpenFlights.org isn't helpful, as it is not accurate enough. Obviously though no one can fully predict exactly where an aircraft will be in the future because that changes in respect to many different unknown variables, but I need something more like this, which was done tracking one commercial jet from one airport to another which includes no amount of variation, and it takes a long time to do this live.

Ideally I could get the general routes that these individual flights tend to follow, but to get an approximation of the actual routes between airports would be a whole lot better than I am know. 

In a perfect world there would be lat/lon/alt/ pairings of the paths with some sort of standard deviation on those points. I doubt that exists but anything that could get me closer to that would be excellent.

Paying for something is not necessarily a problem, as long as I can prove it to my boss that it is what we need.
Yes, depending..... 
On FlightAware.com you can see the routing of a flight after it's flown, and the same flight the next day will probably file for the same route.

On FltPlan.com you can find typical routes that a plane is likely to be cleared on and have actually been cleared on over time. Pretty accurate, but you probably need flying skills to interpret it, or get training on understanding routing, airport ICAO codes, nav fixes, departures arrival and enroute routing.