iTrip ease of use / alternatives
My wife and I use the auxillary input on our car and just plug a standard cable from the phone or iPod to the car that way. Newer cars have the auxillary input moved away from the radio, ours is down below the radio and dash. This is by far the cheapest and easiest solution.

If that doesn't work you could always buy an FM modulator, but sounds like you tried that.

My best recommendation, which sounds like it isn't up your alley, would be to buy an after market stereo that has a direct iPod/iPhone connector. These work great because you can control the device from the car stereo and not have to fuss with the device once plugged in! Alpine has one of the best for this and is one of the top car stereo manufacturers. If you do go that route, buy from Crutchfield...