Can't afford an svc 350 but the best sound coming out of my hardware vocoder is provided by the Korg Poly-61M - tried others but keep coming back to that. It's not such an expensive synth either.

i mostly use an unfiltered saw wave. pure and clean without filter resonance. tryed one from an juno60 osc, ms20 osc or whatever. u can also use one from your vst instruments. for better robot sounds i put a an on and off switch( its a guitar switch, ca 20Euros at your local music shop) in the ensemble jack. you turn off the ensemble mode from the svc 350, wich is always on when nothing is plugged in. turn the ensemble off and it rocks much better for robot voices. someone did a really good instruction video. http://www.youtube.com/watch?v=cOO6xTXTeiA

try with TAL-U-No-62

kunz.corrupt.ch/products/tal-u-no-62

White noise.
Guess what that can be used for? (hint: "aaaaaghh!! This stuff is really fresh!")

I like using MKS-50 (rack mount Alpha Juno) with the pwm'd saw with a bit of noise mixed in. It's been the best carrier I've used. But, I use an Eletrix Warp Factory (or Ableton's vocoder).