Gouda wrapped in a Phyllo beggars pouch and baked, served with crackers and fruit - always impresses my guests and super easy.
Anything with shrimp. For my daughter's engagement party, I made shrimp "shooters" - shrimp cocktail in tiny little cups. VERY well received. (the ones I did had one med/lg shrimp per cup with cocktail sauce, lime and cilantro. I rimmed the edge of the cup with seasoned salt)
Caprese kabobs have also been a hit. Skewer grape tomatoes, tiny fresh mozzarella balls, basil and serve with basalmic vinegarette to dip.
Any kind of stuffed mushrooms. Super easy and very popular at my parties: mushrooms stuffed with onion and chive cream cheese topped with parmesan and broiled. But I also get a lot of compliments on my breadcrumb stuffed mushrooms too - not quite as simple, but still pretty easy. (bread crumbs, celery, onion, tumeric, butter)
I'll post again if anything else comes to mind. Good luck.