Replacement CD/stereo for 2002 Dodge Durango SXT?

Considering purchasing a used 2002 Dodge Durango, but before I do, I want to know a good site to buy CD/stereos that will specifically fit the unusually shaped dash. Also wondering if a later model Durango CD/stereo will fit the 2002 model. Also, wanting to make sure that the new CD/stereo supports MP3's/WMA's. If I get the Durango, I would need to get this stereo installed professionally, so national businesses that sell/install such aftermarket creatures would be appreciated as well. I'm not really a car person, so I'm at a loss on where to begin.