I have a Sidisi, Brood Tyrant deck that is all about utility creatures, ramp and then massive token armies from swelling the graveyard with dredge. That said, I have a LOT of useful cards in Green/Black and even some in blue.
I have a lot to say, so it comes in three parts.
Recursion:
[[Eternal witness]] [[Skullwinder]] [[Nyx Weaver]] [[Golgari Thug]] [[Riftsweeper]]
A deck that's focused on the graveyard needs repeatable ways to recur threats and reap value through the graveyard. These are the low cost recursions I have that are stapled onto creatures in the deck. Each functions very differently from one another. Eternal Witness is the most straight forward of the bunch, and gets back anything.
Skullwinder I find is actually a great political tool in the early and mid game, where you can aid other players or leverage your graveyard to theirs for favors or exchanges. Never underestimate political moves in EDH. Sometimes giving another players some benefit will end up helping you more in the end as they join your side.
Nyx Weaver is an enabler for the deck, allowing you to stack more mill triggers and fill your graveyard with goodies. When you need to get something back, you just pop him for it. He's not as easily recurred, but having that dual purpose of mill and a regrowth on a stick is more than worth it.
Golgari Thug is a powerhouse if you have [[High Market]], [[Phyrexian Tower]] or [[Grim Backwoods]] in your list. He allows you to get back key parts of your deck's strategy, setting up armies with [[Avenger of Zendikar]], overunning with [[Cratherhoof Behemoth]] again, or just fetching back other useful utility or ramp creatures. He can be a bit difficult to utilize if you don't have a sacrifice outlet ready, but if you build them into your deck, it becomes a strong, consistent, but slightly slower engine than some of the more instant speed regrowth effects.
Riftsweeper is an oddball. What on earth is it supposed to do? Well, when you're in the late game and your entire graveyard has been exiled, I'm betting that exiled Avenger of Zendikar is looking pretty good right now with the 20 or whatever lands you have. Or maybe you just need to get back a wrath, or something else important to dig for. Riftsweeper is my deck's last "catch all", which allows you to get the engine rolling again after being beaten down. It's saved me on multiple occasions.
Ramp:
I know you didn't want mana dorks in this category, but never underestimate the power of fetching a land or a mana dork with additional abilities. Land ramp stapled to creatures that can be recurred is powerful and difficult to disrupt, which lets you accelerate into the late game much more safely and explosively.
[[Deathrite Shaman]] [[Diligent Farmhand]] [[Sakura-Tribe Elder]] [[Yavimaya Granger]] [[Wood Elves]] [[Farhaven Elf]] [[Yavimaya Druid]] [[Somberwald Sage]] [[Fertilid]] [[Burnished Hart]] (I know it's cheating)
Deathrite is called a 1 mana planeswalker for a reason. Not only is he consistent ramp (you're playing in black green, you're going to have lands to exile in the graveyard) but he's also an incredibly useful tool for keeping yourself healthy, punishing enemies for plays against you, etc etc. He's not only a mana dork, but he's a swiss army knife with a degree in diplomacy.
Diligent Farmhand is another oddball. He's not quite a mana elf and he's not quite a Sakura-Tribe Elder. He's nearly as good though, since he comes out on turn 1 and does something you want to do on turn 2 anyway: Ramp! Additionally, he becomes another body in the yard that you can reuse or use for graveyard shenaniganry.
Yavimaya Granger has some of the same quirks as his farm buddy. He just grabs us a land on turn 2 or 3, then he becomes fodder for our graveyards. We don't even have to sacrifice him or get him killed, he does it on his own! Yay!
Wood Elves, Farhaven Elf and Yavimaya Druid are all in the same spot for the same reason: more consistent ramp on sticks. That said, some of them are better than others. The best of the three is Wood Elves, as it allows us another mana to use this turn should we need it to play another small creature or spell. Additionally, you can search for dual lands with basic typings! Yavimaya Druid is next, as it also allows us to search for a dual land with basic typing. Farhaven Elf is the worst of the bunch, but by no means awful, it's still ramp on a stick.
Somberwald Sage is perhaps one of the best low drops in green creature decks. It not only allows you to fix your mana on the fly, but shoots you up to 7 mana on the following turn. That's big enough to play a fatty tutor like [[Rune-Scarred Demon]]. There's never a hand I don't keep with the bird sage and at least 2 lands. The opportunity she gives you to reach midgame is too big.
Fertilid and Burnished Hart are the power land fetchers I have in my deck. Both search up 2 lands for the cost of 1 card. Sure, they might be expensive, but they push you from mid game to late game is just a few turns. As with all the other land rampers previosly mentioned, you can use them over and over again by getting them back from the graveyard. If you have any counter sub-themes, Fertilid just becomes absolutely bananas.