A friend pointed out this neat itinerary planner for the 3 Valleys (click on the "Taylor-made 3 Valées" banner). You tell it which resort you want to start (and finish) at, your level (expert, families or "fun") and whether the weather is sunny or cloudy. It then suggests a route taking in the whole 3 valleys (high or low depending on weather) and gives you a PDF route plan like driving directions to print off.
It is a pity it does not tell you the vertical gained and lost with each run and the distance to ski, rather than just an overall estimate of the time required, but its fun none the less.