Everybody has a favorite insect, but I doubt many people would admit they love flies. Mosquitos, gnats, and no-see-ums are all Dipterans (the fly order) and they're all fairly well disliked. However many fly species play important roles in our world. Some are decomposers who play an important role in forensic science. Some are important pollinators. Some play a role in genetic engineering. Unfortunately, what they're known for is spreading diseases like malaria, yellow fever, dengue, and encephalitis. Love 'em or hate' em, they are important participants in our ecosystem.
I don't have many pictures of flies, even though I see them all the time. Here's the best of what I have...
Green Bottle Fly (above and below)
A fly next to one of its favorite foods, bird poop!