How do I buy RAM, The good ones.

I don't know shit about Ram, is there a site that explains the difference between them and features some of them have, like the dual channel and stuff.  SAVE ME!!!!!!!!!!

This may sound ridiculous, but there's a good introduction to different types of RAM on Wikipedia - just type in RAM for the search - the types are listed to the right of the page.
After that, then go to somewhere like Ars-technica's guides and forums to see what manufacturers they're recommending at the moment.