RMC, Wizzard wah and T-Rex delay are two which I like and don't alter the tone at all. Exotic o/d are ok but I find o/d pedals generally cut too much bottom end.
the only thing i run in front of the amp is my ernie ball volume pedal and the tu-2. the rest of the effekt-chain goes into the insert of channel 1 of my vh4s.
gonna get shit for saying this but I use a Dunlop CFH Dimebag wah. Since the components are not designed to emulate the vintage wah tone (like the RMC stuff), it's a lot quieter. Also the 5 way sweep switch has TONS of variation. Ole Dimebag KNEW how to design a wah pedal for HI-gain use.
If I could ever get the ground loop and noise issues solved I'd be using my Fractal Axe-FX for pre effects (comp, wah etc) as well as the post stuff...
I the serial loop of the Vh4, the Boss GT-10, using the 4CM but had to tweak the hell out of the S/R's on the GT-10 to preserve as much transparency as possible. The Vh4S, just a GC for channel switching and a Boss Super chorus in the Channel insert 1.