Not the little flower faeries from the Victorian period, or Disney's saccharine versions, but the old ones, the lords under the hill and the ladies across the water, to name but a few. The joy of the Faeries is that they're wonderfully diverse, where vampires and werewolves tend to fit into a single template, or at least with only a small number of differences. Faeries spread from pilliwigs, which yes are flower faeries, all the way to the Redcaps of the Scottish border, the Cornish Nockers, and the Sidhe or Tuatha de Danaan. Every culture has its own folklore of spirits and stories, often cautionary tales that were intended to guide people on ways to behave if they encountered things outside the ordinary. They also informed the ways that men and women behaved and saw each other. This became especially true when the Grimms collected and updated these tales for the modern world, a trend that has led us to Disney and to Angela Carter's revisioning of them. As fairy tales became modernised they also became prescriptive, laying out more obliquely how men and women should behave, acting as socialisation tools for the bourgeoisie.
Dialling things back, it may be that the myths about faeries may stem from earlier versions of humanity, the bronze age dwellers who did not adapt to the iron age when it rolled into town. They may have been people who lived under the earth in barrows. As a result, the new settlers from the east, the Celts and others, may have seen them as something supernatural. Bodies of mythology grew up around this idea, and in Ireland we can see the idea of waves of settlement and development, as the Firbolg settle the land, and are displaced by the Tuatha de Danaan and their followers. That would seem to support the theory and to give an idea of how the concept spread. In addition, there are many old gods hidden among the ranks of the faeries, often in the form of the Green Man or similar figures. Of course, they are the only places that pagan gods ended up, many became Catholic Saints as well.
The other angle I love the fair folk from, is, of course, Shakespeare. Midsummer Night's Dream is amazing and as it's the solstice today, it feels particularly appropriate to mention the play and the wonderful monologue by Puck at the end. I'm also rather taken by the Cottingley fairies story, which fooled Sir Arther Conan Doyle.
The fair folk also make a strong showing in Neil Gaiman's Sandman series, which portrayed Auberon and Titania in a colourful, if not entirely sympathetic light. Gaiman was one of the writers who brought the faeries back to their capricious selves. That's something else I like too, the idea that they are not always our friends (and I can't stand the hippy drippy version where the faeries just want to be our friends).