Not sure if this is too broad, but I am currently in the process of making a few flying alien species and, of course, didn't want to use the old insect or bat-like wings.
Of the types of wings (or flying surfaces) I can think of present on earth, there are the limb-bound wings using finger bones for support with skin membrane in between (bats and pterasaurs), small limbs with growths to provide more surface area e.g. feathers (birds), vein-ridden insect wings and the simple gliding surfaces of some mammals (skin flaps of some possums and squirrels) and lizards (outward facing sails on draco lizards).
While this is quite the list, to achieve a more 'alien' powered flight I need a different structure. So basically, is there another possible structure for wings used in powered flight? (not looking for biological jets, sky-rays or whale-blimps).
Edit: I have developed two different groups of creatures to fill the large animal niches of my planet, which are the mammal-like quadrupeds (four limbs) and the reptilian-like hexopeds (six limbs), the latter of which I favor as a candidate for the flyers. They have the typical spine, defined head and a rib-cage-like lattice with vital organs encased. Their environment is much like earths, but with a slightly denser atmosphere, so I'm guessing their size could vary from quite small (bee hummingbird) to larger than Quetzalcoatlus. I do want powered flight, so flapping is most likely essential.