I bought this one back in March. The price seems wonky now, I paid about $17 for it.
I have it set for 87.7, and my car stereo set for that frequency. It actually works “OK”.
Is it perfect? No. I also don’t live in a huge urban area with tons of radio stations bleeding over in to that frequency.
This particular model does NOT act as a charger for the iPod (some do), that might be the only downside. I think it’s worth $17 to see if it works for your situation.
We’ve used a Griffin iTrip going from DC to Massachusetts and back. Worked pretty well, even around NYC, and only had to change frequencies a couple times. Having a traveling companion to mess around with the transmitter & radio really helps.
'Course, maybe the OP switched cars in the past couple years. 
I have a Jabra Cruiser bluetooth handsfree kit in my car. It pairs with my phone and allows me to do handsfree calling (with the right phone, it can also send texts, etc). One of the features is that it also acts as an FM transmitter for the radio, so you can listen to callers over the car speakers (not sure why you want to do that, but you can). It also works well when the phone plays music. So if you have bluetooth, that’s an option.
I use it over the Aux input on my radio because I get a high-pitched whine from the aux input.
Similar products are available from Motorola and many other vendors. Check reviews before buying…