Looking for a recipe for an amazing, innovative mostly make-ahead appetizer.

You could try empanadas; a simple oil-based dough and a savory meat filling (chicken, shredded beef, etc. Also, there is a whole repertoire of Spanish or Sephardic savory pies, small and large, incorporating things like cheese, roasted red peppers, tomatoes and eggplant, etc. in Claudia Roden's and Gil Marks's books on Jewish cooking.

The most amazing appetizer I ever made was the Couscous Waffles with Roasted Red Pepper Dip from Dorie Greenspan's "Waffles: From Morning to Midnight". If you don't have access to this book, I wonder if Dorie can post it.

I often make a seafood layer dip. Bottom layer is cream cheese, sour cream and a bit of mayonnaise. On top of that spread seafood sauce that has a bit of sriracha mixed into it. Next addn flaked crab and/or tiny shrimps. Then add a layer of shredded cheddar or colby jack cheese, and top everything with an equal amount of finely diced yellow bell peppers, tomatoes, cucumbers and scallions. Serve with substantial crackers or pita chips. Pictured in the centre of the photo as part of my Thanksgiving appetizer spread :)

Other ideas: falafel and tzatziki dip; gyoza with soya and vinegar dipping sauce; mini samosas with mint and tamarind chutney.

Asian shrimp toasts can be made in advance and broiled as guests arrive. Bruschetta is also great made in advance, especially if you set up a "bruschetta bar" so everyone makes their own.

Thank you for all these great ideas!

What's the theme? If you have time...test out getting some 'rice paper wraps' these are the wraps you get for uncooked spring rolls (the ones filled with shrimp, basil, cabbage..etc).
The question would be if a 24 hour make ahead would work with those---easy enough to test out make a couple with some shrimp or just veggies..and store over night. They're served cool.
Maybe layer in a bit of Hosin sauce to make up for lack of dipping sauce at service.
........and then we get to maybe some peking duck in the wraps.
I think that would hold cold. Some roasted duck meat..a bit of cabbage..and hosin sauce and green onion bits wraped in rice paper package. Heck...throw some carrot shreds and use purple cabbage .

I found Olive Al'Ascalona here on food 52. Amazing queen olives, stuffed with seasoned goat cheese, french breaded and deep fried. OMG...Salty, crispy, bursting with flavour. You can also make them hours ahead and then place them on a rack in the oven to reheat and they taste freshly made. Highly recommend for this sort of party.

Not sure how innovative this is, but squash toasts are delicious and I make them mostly ahead and then just assemble. You'd have to toast the bread (I don't fry it but I bet it's really good that way) and spread the cheese, and top them not too far in advance, though. I usually do them on bigger pieces of bread and then cut the assembled toasts into smaller pieces. http://cooking.nytimes.com/recipes/12944-jean-georges-vongerichtens-squash-on-toast

Make mini savory cheesecake tarts.
Use a pie crust (home made or store bought) and shape mini tarts in muffin or mini muffin pans. Blind bake. Pour in savory cheese filling, bake, chill. Serve as is or with a chutney or tart topping, like red pepper jelly.
Could do own filling (any cheesecake without the sugar and use some savory cheese mixed with the cream cheese) or one of these two:
Fig pesto mascarpone
Epicurious.com/recipes/food/views/Fresh-Fig-Mascarpone-and-Pesto-Torte-13233#ixzz1ow5axvks
Stilton cheesecake
http://www.epicurious.com/recipes/food/views/stilton-cheesecake-with-rhubarb-compote-103409
Idea from my mother, who used to make mini-sweet cheesecakes for parties.

My favorite appetizer (and snack) is Pancetta crits with goat cheese & thyme. http://www.epicurious.com/recipes/food/views/pancetta-crisps-with-goat-cheese-and-pear-231265
I've been wanting to make the cheese ball style turducken but don't have plans to make it for 15-20 people. http://www.chowhound.com/recipes/the-turducken-of-cheese-balls-30216

Another appetizer thathttps://food52.com/recipes/21537-spicy-korean-style-gochujang-meatballs great warm or at room temperature is foxesloveslemons Spicy Koren Meatballs - Yum but read the comments for heat level opinions! https://food52.com/recipes/21537-spicy-korean-style-gochujang-meatballs

I've made these as well : https://food52.com/recipes/39379-fig-manchego-and-honey-pastry-twists

One more: "Baked" Salami with Mustard http://www.tastingtable.com/cook/national/how-to-make-an-easy-party-appetizer-with-salami-mustard You can just keep warm in a low oven or reaheat meat in the microwave.

Gougeres are fun and delicious, they're always the first to go.
Toast crisps with fresh apple, brie cheese and fig jam is my personal favorite (and occasionally my dinner!)
Baked Brie can look beautiful, pretty sure it can be made ahead, similarly baked goat cheese is delicious!

I saw a recipe once for a soft pretzel which is stuffed with a spinach artichoke dip, the pretzel dough is rolled out real thin, the dip spooned in, the dough folder over and pinched shut, then tied in the pretzel shape. Then baked. I haven't made this, but I want to. I don't know how it would work with smaller pretzels. I wonder if you could do it with one giant pretzel for people to cut off pieces and eat? Anyways that's an unexpected idea IMO