[snbush67]

Seems you have ruled out the grounds, the solenoid and the battery. I was quite sure it would have been your ground.

As a few have pointed out it seems that the next most likely thing is an intermittent issue with your electrical portion of your ignition switch.

A common problem here is corrosion or wear. One way to possibly check is to wiggle the key, or hold pressure on the back of the switch while you are turning the key to see if it engages. If it does you will see that, the switch is the problem (or part of the problem) and needs replacement.