How do you connect an iPod to your 1999 Toyota Camry?

There are at least three ways. First one is to use a cassette adapter and use 1/8 inch jack in your Ipod. Second is to get a FM transmitter and tune your car radio to the required frequency. And third one is to use AUX port in your radio (if you have one) and the Ipod's 1/8 audio jack.

Stay away from FM transmitters, they don't work on Toyota radios because there is no antenna, the antenna in most Toyota vehicle it in the rear window

The best way clear and digital to input audio from your iPod into the Factory Toyota radio is by using an auxiliary audio input interface, this is only available in the 2008 and up models , the good news is that you can add the aux jack and interface to almost all Toyota radios from 1998 and up to find the correct kit

just do a search for ( Toyota auxiliary interface )