I want to buy some more DVD-R's for my new iMac, but I don't want to necessarily buy them from Apple authorised dealers [looking for better prices]. What do I need to know to make sure that what I buy ...

I know this has probably been asked before, but allow me to do it anyway. What is the technical differencies between dvd+r/w and dvd-r/w, and how does it differ practically when using the media in ...