fungi have already demonstrated the biological complexity necessary to zombify animal species. (insects are part of animalia.)
Something akin to ringworm that sends its mycelia deep into the peripheral nervous system, then follows those nerves back to the spine and then up into the brain would lend itself well as a potential zombie pathogen.
Viruses look neat to hollywood, but their genomes are small by necessity. Fungi on the other hand, bring exotic biochemistry and functional biological hardware to the table, and already have demonstrated real zombification powers.
The digestive action of the fungus on the host could well produce "rotting corpse like" features, and neurological changes from having the brain infiltrated by mycelial fibers could produce the aggressive behavior. Being predominantly a skin infection (in the case of ringworm), having its victims claw into the skin of healthy humans would spread the contagion by direct introduction under the skin via the scratches.
Early stages of infection would be terrifying, because behavioral changes would come much later, but symptoms of the skin and peripheral nervous system (like uncontrollable itching/burning sensations, causing people to scratch) would manifest early, leaving the poor host to have ample time to contemplate its fate.
If I were to engineer a zombie plague, bioengineered skin fungal infection (resistant to all major antifungal medications) would be my vector of choice, with genes harvested from the fungus that zombifies ants and other arthropods.
I think that could actually work.