Starting Problem?

Riddle me this...
Every now and then, my SC won't start up. Turn the key, and nothing. No sound, no click, just nothing. Had the battery checked and its ok. Its not the starter relay, either. Now, I can jump it at the relay to get me going, then its ok for a while.
ANY ideas out there?
Thanks guys.

Ignition switch...

Just a guess.

Hehehehe.. how are your brake lights when this happens?
The 90 year has a little feature where the stop lamp switch is part of the starter circuit. Next time it doesn't work, don't let off the key.. push the brake pedal up/down a few times to see if it suddenly comes to life.

clutch

try your clutch safety swith if its a 5 speed. Mine went...and the the starter didn't do anything....easy fix though. I just plugged in a code reader and it told me it was that....good luck!