Mods, can you change the thread title? I only just looked at this because OP's title didn't attract my attention.
I think CN forum user GreggGermer runs a place around Oudenaarde.
People here talk a lot about the classic cobbles of the Ronde, E3, Het Nieuwsblad, KBK etc, so I'll drop in a few words about how things are further east.
The roads criss-crossed by Liège-Bastogne-Liège and Flèche Wallonne are generally pretty quiet. They roll through a part of Belgium that's not particularly well-known to folks who don't do much outdoors.
Côte du Rosier, from LBL
I have hiked extensively in the region, so I know it pretty well and I would recommend that if you have the time and the means, the eastern Ardennes provide an exciting counterpoint to the perhaps more familiar bergs and spired towns of Flanders.
Côte de la Redoute, from LBL
The deep clefts and woodlands of Wallonie are full of secrets and strangeness. One gets the feeling that the annual passage of the peloton in April is almost the only thing to disturb the silent greenery of areas like the Ourthe Valley.
Mur de Huy, from Flèche Wallonne