GTA Stereo upgrade

Hi,
I would like to replace the original stereo in my GTA with a new more usable unit, I would like to have GPS and a reversing camera as well. Is there an upgrade that someone has done or a unit that might be easy to fit and wire? I doubt if there is a plug and play model on the market but you never know.

Thanks,
Paul.

These are meant to be pretty good.
Not that I've tried.

http://xtrons.co.uk/head-units.html?p=2

What are you doing with the old one? - I'm looking to go back to the 80's!