There are many paths for this and it all depends on what you're actually trying to do. As a few have said, the audio forum has a plethora of information.
What it really comes down to is this question: are you keeping the stock HU or are you replacing it? (assuming that you have the climate control and not the base HVAC system)
If you're going to keep it:
- wiring harness to add subwoofer connection (normal line), and you'll need a lineout converter or an amp that can handle it.
- Jazzy mod to allow use of mp3/ipod.
- Scosche mod which connects directly via the antenna vs just using a transmitter for the mp3 player.
If you replace it:
- AVO JDM HVAC (~$350-400 US) for Double Din
- New Stock headunit (07-09) which allows has an MP3 connector
- Cubby pod mod which allows you to use the stock HVAC unit.
There are a few more, but they were extremely difficult or didn't fit what I was looking for.
As for me, I was looking to spend the same amount of money for a new headunit, so I bought the AVO JDM HVAC and modified a crutchfield single din kit (for the base leggie) that came with my stereo. This only required cutting the kit and nothing else. You can see a picture of it in my album here: http://legacygt.com/forums/album.php...pictureid=4289