You have come to the right place, young whippersnapper. There are many on this board that would rather watch Het Volk on the telly, than watch the Tour from Lance's rear pocket.

I'll give a quickie and let others add on.

Basically two types of one-day classics. The cobbled kind and the hillier kind.

Cobbled equals just about everything in Flanders and Northern France.
Hillier equals stuff in the Ardennes and Italy.

There are of course great one-day races in other countries besides Belgium, France and Italy, but none of them have the same incredible history (although the Amstel in Holland has become quite a biggie).

Hmmm... droool... classics... neeeeeed fix nowwwwww...