One of the best, relatively new, features on the modern stereos is a USB port. This way you can buy a thumb drive(also known as flash drive), copy all your music folders from your computer to the thumb drive, and plug it into the USB port in the car stereo. I bought an 8 gig thumb drive, about the size of a stick of gum, from Microcenter for $15. I've figured that little 8 Gig thumb drive will probably hold about 70 CD's worth of music on it. This is the most inexpensive and convenient way to carry and play your music collection that I know of. No CD's or Ipod needed.
I installed a Kenwood KDC X492 in my 79 last year, which has the USB port on the front, so I just plug the thumb drive in and play. It will play a CD if I had to, but all I use is the thumb drive. There are newer Kenwood models available now, and other brands that have USB ports too. Some have the USB port in the front...some have it in the rear for use with a cable. And they'll play an Ipod too, if you already have one. Of course, these stereos come with a remote control, which I like to use. And they have good power. Mine has 50 watts x 4. There are some good looking units out there, with attactive lighting, design and graphics. They have many good features, and they don't have to cost very much. I paid about $125 shipped to my door.
So, those are features I looked for, as well picking one that I thought would look best with the style of the TA. I think the features are worth making the hole for it

.