I'm looking at replacing the stock radio with an aftermarket one with a CD and ipod input, but I have a few questions first before I buy one.
1. What brands of aftermarket radios will fit my discovery?
2. What other things (cables/adapters) I would need in order to make it fit?

Here is one that I'm considering.

Amazon.com: Sony CDXGT340 MP3/WMA Player CD Receiver (Black): Automotive

 

Two ways you can do it. One is to integrate the current amp and wiring in which case you'd need a harness adapter special for our trucks. Crutch field has them for like $20 or you could (recommended) bypass the factory amp by splicing into the head unit and running new speaker wires to the speakers. So in theory what you'd need is a special harness or 40 ft of speaker wire. Any single din receiver fits us I believe.

 

Crutchfield: Car Stereo, Speakers, Home Theater, LCD TV, Digital Cameras
Fill out the vehicle info, everything you need will be included.
I bought my Kenwood unit at BestBuy, they installed it for free and bypassed the amp.
No need to run new speaker wire, there is a wire harness that you can buy (Crutchfield.com) that will by-pass the factory amp but still use the factory speaker wires.

 

I have a Kenwood KDC-148, cant complain

 

We ditched our entire factory system and just ran all new wires. The factory wires are so small and poor quality it doesn't make sense to leave them intact during an upgrade. We decided to add a 5 channel amp as well which was a big plus. If all you want is a new head unit though the crutchfield harness is easiest.

 

Important note: D1 has two antenna cables, each goes thru individual amps in head liner above rear fixed glass side windows, antennas built in. Both will do FM, but only one is AM/FM. My PO made the wrong choice.... can't get AM. So test before final close up.