Query: After-Market iPod Connection?

So, back in November, I bought a new car, which came with a six-month free trial of Sirius Satellite Radio. That’s about to run out, and while it does have its good points, I’m not really interested in paying money to listen to the radio.

What I would prefer is to be able to play my iPod in the car. Which I can do at the moment, using one of those little FM transmitter things. The problem with this is that it requires a clear FM frequency to work, which means it’s essentially useless in any major metropolitan area (or at least in Boston and NYC, which are the cities we visit most frequently)– there are no FM frequencies in NYC that don’t at least have a lot of interference from nearby powerful stations.

My question for the Internet, then, is this:

What is the best way to directly connect my iPod to the stereo in my car?

I’m guessing that it must be possible to get a car stereo that has an iPod input, or at the very least an “Aux. In” jack that I can plus the iPod into, but I don’t know anything about the options. Somebody out there must, though, so if you do know, leave a comment.

(It would be nice if whatever the solution is allowed me to continue using the stereo controls on the steering wheel in my car, but if I had to live without those, I could.)