If a new key works fine, then you probably just need to get a new master key for your car. I agree with the comment about the passenger door lock.

If you start to have intermittant problems turning the ignition with a good key, then you want to head over to the dealer/shop soon, and if it is at all safe (i.e. unlikely to result in your car being stolen), to leave the key turned halfway in the ignition. Removing the tumbler requires the key to be in the ignition, and turned to one of the positions. Without this, you have to drill out the center of the tumbler...