Had a bit more of a search using a variety of terms, unfortunately the search function doesn't like the term '0-10v'.
Is this the kind of thing most people are using?
http://ruggedcircuits.com/html/circuit__20.html
No... An op-amp won't have the current capability to turn a valve. And, if you can use PWM (which I assume you can), you don't need an "amplifier".
If you use a MOSFET (I can't find a schematic at the moment 
), then the only trick to getting the 10V maximum is to use a 10V power supply. The power supply sets your maximum, and the PWM setting sets the faction/percentage of that maximum on a scale of 0 to 255. For example, if you program the PWM for 50% (128) you will average 5V, and the valve should go to the half-way point.