Aftermarket receiver options?

I am upgrading my cassette player to a CD or CD-receiver (undecided which). Have any of you put in an aftermarket system? Is there anything that fits the slot exactly, or is the only option to get a din sized receiver and a bracket? Does a din and a half fit? How is the radio reception after installation?

I upgraded to an Alpine DIN CD player. It's really easy to install and required very minor alteration. So minor that if you decided to sell the car and re-install the factory radio, no one would know. I don't know about the DIN and a half sizes, none of them appealed to me. Radio reception from my Pioneer (old stereo) was terrible, although it is excellent from my Alpine (new stereo).