Since the ME-50 already has a distortion modeler, why not go for a single
distortion pedal? You could try the Boss DS-1, or a Big Muff Pi, etc. You could also look into an
overdrive pedal, like a Tubescreamer.
As for wah pedals, I love my GCB-95 Crybaby, although I recently added a Q control to it, which really increases its versatility. The Zakk Wylde has some nice features, but they don't justify the price IMHO.
As for delay, is the ME-50's built-in delay that bad?