The best route to go is to replace the OEM radio with one that has an AUX input. However this can get expensive and you need to get a dash kit in addition to the radio.
There are several options for adding an AUX input to the stock OEM radio. I too have an 05 with a six disk changer. I use a Macally FM transmitter to run the audio from a Garmin GPS unit through the radio/speakers. Its a cheap, quick and easy, way to go, however the sound quality isn't that great. Others have had really bad luck with FM transmitters and don't recommend them. There are dedicated aux adapters that plugs into the CD Changer port on the back of the stock Corolla radio (including the six disk version). It is possible (if one has small hands) to attached these adapters without removing the radio. You can just barely reach the CD Changer port on the back side of the radio by going through the Glove box. Drop the glove box as if you were going to change the cabin air filter and there is just enough space to reach up behind the radio if you have small hands.
Here are some links to various places that have these AUX adapters.
Crutchfield - iPod/MP3 Car Adapters:
http://www.crutchfield.com/S-YLRaYQY...ers.html?tp=15
PIE Toy 03 Aux:
http://www.logjamelectronics.com/pietoy03aux.html
USA Spec has one for the iPod, they used to have one with RCA connectors but it doesn't appear that they sell those anymore.
http://usaspec.com/product.php?ProductID=17