We grilled 4 types of sliders this weekend for some friends and I think it was a hit! The sliders included beef with tex-joy seasoning, southwestern turkey, pork/chorizo (adapted from here) and buffalo/blue cheese. We also had lots of toppings including cheddar and pepper jack cheese, lettuce, tomatoes, guacamole with bacon, bacon, onions sauteed in bacon fat and others. (See a trend there?)
Other slider recipes:
chili bowl burger sliders (I'm still on the fence about the shaping of meat into a bowl form but I like the idea of chili-like spices in the meat itself)
meatball sliders
lamb sliders (on potato rounds instead of buns)
white castle style sliders
turkey sliders with feta and sun-dried tomatoes