I will second both of Reaper9889's suggestions. Tortured Existence just lets you recur all your favorites and generates tons of zombies at the low cost of one black mana each. It also works wonders with cards like Grave Scrabbler and Golgari Brownscale (which you're already playing). Reaping the Graves is clutch as compared to Death Denied because each copy will net you a zombie from Tormod, whereas Death Denied will only net you one. Once you have that recursion engine in place, I'd also recommend Gempalm Polluter as a means of dealing large chunks of damage without having to attack with the zombie army you amass.