I had exactly the same symptoms with my 93 camry for a year or so until I traced it down. While your problem may have a more ordinary solution, you might check this out. When your car is running, I don't think that the engine check light is lit but despite this there MAY be an error code stored in the ECU from the no-start events. If you get the instructions on reading this error code (from searching this group, say) and the error code is 12 (No G or NE signal upon engine cranking) then you have my problem. I now believe it is caused by an intermittent poor contact in the plug/socket for these signals on the distributor body. To prove this in your case (this seems to work for me) next time the car wont start, turn off the ignition, open the bonnet and do nothing but give the plug/socket on the distributor a good shaking. Now try to start the car. If is does start then you have solved the problem. I have not fixed the problem. I just shake the connection when it wont start (about 1/year).
Good luck