Despite the caveats above, I'm still pretty into the concept of flamethrowers as an anti-zombie weapon.
I don't necessarily think that a large, back-mounted one is your only option either; improvised munitions of the incendiary variety definitely have a place in taking ghouls out. More importantly, you should be prepared to burn the dead anyway, both yours AND theirs.
Also, neurotoxins are an interesting option. If a zombie is walking, it's using its neurological system. Rattlesnake venom, although probably hard to procure in its natural form (and thus making one consider the viability of synthesizing it or using something like it which originated in a lab), could theoretically stop signals from traveling across the synapses of the walking dead.
Good luck injecting it, though.